Might wanna check with Eric at RSM, He distributed them when they were available.

 Steve   
  I have motors # 01 and 007 I ran them a lot for many years. I finally settled on 15-20 oil but no more than 25% castor. I ran them fast with 10/4 and 11/4 props. They will run erratic with castor only fuel. I did away with the factory needle valve set up as it was to big to get in the nose of the plane and went with a ST/ or DS/ needle valve set up through the factory hole. Hole size I think is .272-.292 I will need to measure it. I used double head gaskets. Power can be very high if wanted. They would fly the same plane I use the ST/46 in and the motors are interchangeable. The 46 is a little longer from the front case hole. I ran the muffler in the rear configuration and never had it come loose. I mashed down the front of the tank to clear the muffler. Three ounces is enough capacity to do the pattern. Both motors get hard to start a few years ago so I took them down and removed varnish from P&L and then they were OK again. Both have good compression but one is now hard to restart. I contacted Ian two weeks ago and got price for new P&L. He said $45 British plus shipping. That's a bargain.
  NOTE the crank runs in the case there is no bushing but mine show no wear in the case. Some people complained of fuel coming from the front of the case. I added a return slot to the case on one off mine when I replaced  the  case many years ago after a crash but I never had that problem.
Ed

I'd pretty much listen to Brett as he remembers everything and I can't remember what day it is.

Couple of things though.

The engine was designed around low or no nitro fuels and, as I have lots of fuel in the 10/15% range I added a second head shim that has pretty much stayed in it as it ran fine on the higher nitro fuels with it.

The best combination I had with it was with the Tornado 10X4 on my infamous but short lived Brodak original Nobler made famous in its starring role in the award winning drama, Leave it to Shareen.  It was less happy with that prop on the lower aspect ratio Ruffy (much draggier in maneuvers) especially at warm, higher altitude Tucson and a higher pitch three bladed five pitch made a happier combination.  I stole such a prop from Colonel Trostle and never gave it back, a Chinese manufactured wood 10X5 three blade

After operating it for a number of years in the Tucker, the smushed Nobler and the Ruffy I was bored one day and actually read the directions that came with the engine.  The designer/mfgrs of the dang thing suggested the use of all Castor lubricant despite the fact it is an ABC set-up, probably because of the lack of a true bearing interface between the crankshaft and the case if Eddy R. is correct about the lack of a "proper" bearing.  Wearing a full face mask to obscure my action I bought a gallon at the LHS and found it acted much the same way all castor fuel does in a Fox .35, giving a solider four stroke performance.  Had to buy more paper towels, however.

Also, like EddyR, I've never used any sort of "locking enhancement" on the crankcase/header/muffler joints and haven't had an issue although the use of the sealant Brett suggested would certainly be a worthwhile "just in case" given the multiple "fixtures" between the crankcase and the muffler outlet.  Speaking of which... Always be very careful when mounting the side or rear exhaust header between the exhaust and the muffler itself.  It is a very precise fit and goes far enough around the case that you must be sure it is properly seated with respect to the threaded holes in the case before installing the two screws that hold it in place lest you strip the case.

One odd thing that I did find useful was to add a layer of ~1/8" balsa on the bottom of the tank to insulate the fuel from the heat of the header/muffler on a fully cowled installation as there was some tendency to richen up as the tank emptied which I attributed to lowered viscosity of the fuel as it warmed.  It seemed such a good idea that I've since used the same trick on my "pro" stunters; like the built in 1991 Trivial Pursuit (now OOS due to redesigning its nose section along with my left the thumb and index finger with what was left of a previously perfectly good Brian Eather three blade) and the 1985 vintage Citation V  which I'm now hoping to utilize should I ever choose to put Paul, David, Brett and the newly minted WC back in their places.  I've noticed them all getting a little cocky of late.

Were I to actually try to refine the little .40 I think I might take heed of EddyR's preferred way of running with even lower pitched props in the 3.5 to 3.7 range revving up to a very strong four stroke which it should hold around 10.4RPM or so giving a solid 5.0 to 5.2 lap on the usual Classic .35 ship line lengths.  Our late good friend Don McClave had a beautiful flying Nobler with a Fox .35 running that way which was about as good a classic combination as I've ever flown...good strong four stroke full time with none of the infamous Fox heebie jeebies.  His Fox did, of course, have all of the aftermarket goodies as well but it truly seemed the steady "very" strong four stroke and low pitch was a killer combination.

TMI...sorry.

Ted

Thanks to all for the info. Much appreciated.    Steve

At last!! I found this again. Apologies, we've been unbelievably bogged down with other biz. I hope we've got this behind us now.
One thing I notice is that several people seem to have different favourite setups for these engines, and all claim they run right.
Personally I use them as supplied, on an 80/20 mix. If the oil is all castor I find the starting a little easier. If it's 10/10 synth/castor, I never fail to start o.k. but it takes a little longer. It may sound silly, but I should fly more and gain more experience!  I've been flying a little Vintage and Classic Speed lately, but intend for 2017 to include more stunt, at least 50/50.
At VSC I was on the 10/10 mix, and it took a little more flicking than I was used to, but still reliable.
The 51 and the 61 use different c/cases.
If anyone is waiting for anything from me please let me know.