The definitive online Fox Combat engine history is at
http://www.clcombat.info/foxhistory.htmlI'm not exactly sure what you've got there, but it's not a 57 CS. Maybe it was originally, but it's not now. See the gap between the top of the cylinder casting and the head? The 1957 35 CS didn't have that gap. Generally the gap is a dead giveaway that the engine is really a Fox Rocket .40. Given that the case has the removable venturi insert, no lugs towards the front of the case, and apparently no Rocket emblem on the bypass (since that would be really obvious), it's not an original .40 either.
Fox used the O&R type drive washer on the early stunt engines between the tapered seat and the typical Fox 4 cog drive washer, but by the time the combat engines came around they had switched over to the thick steel drivewasher. The O&R washer will work, but the later Fox washer works better. The prop washer isn't right for that engine either, the right one wouldn't have been knurled.
The spade tipped needle, and for that matter the later fully tapered sport 36 needle are an endangered species. They can be found, but not that easily. The normal Fox stunt spray bar is too short. The closest somewhat modern Fox nva that would fit is the big 40 assembly. A small Supertiger nva should fit perfect without any spacers or shims.
Your assessment is correct, just about none of the important parts interchange with the 35 stunt. The crank didn't use a pin. Even with the wrist pin hole, the liner has to come out before the pin can be removed. The hole is necessary because there isn't enough room to slide the rod off the crank pin with the piston still on the other end of the rod.
So what is it? Maybe it's a 57-62 Combat Special or Rocket 35/40, or a 29X case, with a different set of internal parts. Someone could have dropped any of the baffle piston 36 piston/liner setups in the earlier case, which would result in a gap just like that. There's also an early 36X thick head shim/gasket that would make the gap larger if it were installed in the earlier 35 on accident. I don't do the .40s, but most I've seen look to have a larger gap. Could always measure the bore and stroke.
The early Fox combat specials and derivatives aren't terrible engines. They do like to shake, worse than a stunt 35, and they won't run like the stunt engine in a 4-2 break style. They prefer to be run faster with a smaller prop. The lapped piston/liner is a bit fragile, they need lots of castor and hard use is hard on them. By far the problem I see with them is that they tend to wear. I've got a few complete engines, and a few spare cases that all have rub marks inside the case at the bottom of the crank's throw. The marks are from the connecting rod rubbing at BDC. It doesn't really matter if it's from a sloppy crank bushing or an egged out rod, it's pretty much a design flaw. There's zero spare parts support. Fox changed the early combat engines almost yearly, a variety of Fox liners will slide into the case but most aren't exactly the same. If you desire a stunt engine, a stunt 35 would probably work better. If it is a .40 it might be workable with an extra head gasket, etc but it's probably not worth messing with. If you paid less than $25 you can probably get your money back out of it on Ebay. It might make a decent sport engine assuming it's not worn out.
For reference, here's a 1957 silver head CS, the needle is wrong but the rest of the parts are original.
1958 black head CS.
1960 red head Rocket 35 (note: I don't have a 1959 RH Rocket in my collection).
1962 silver head Rocket 35.