I've recently acquired this OS.29 that has a rear mounted needle valve assembly. It's in excellent condition and doesn't appear to have ever been run or mounted. I don't expect that it's a super rare find, but I'm not sure if I've ever personally seen one. Can anyone here fill me in on the vintage? Any other information on this engine would be appreciated as well.

 Thanks!

O.S. factory item. O.S. 29-X. Should contain some special parts, - can't remember off hand. Nice.
Sometimes called Custom-X?
Anyone got a 35-X available?

1961 29-III X would be my guess based on the plug location. It's a max-III and the one I got is a max-II mine is a 1957 29 II.
hope this helps

Peter Chinn in the Brit. mag Model Aircraft reviewed this motor, maybe over a couple of issues.
I think one feature was a couple of small holes in the piston each side of the wrist pin to allow oil to seep through the holes and lubricate the cylinder walls. And maybe a special rod.
Another identifying feature is that the exhaust is not tapped for silencer fixing. If/when I find the mags, and hoping I remember, I'll post details.

Oh yeah, super rare.  

(Sorry Wayne. Couldn't resist. I tried.)

Clint,
I may be wrong, but yours looks like a 1959 os 29-III
to me. Basically the same thing.
Sorry to intrude guys, but I'm a huge OS engine nerd! It's all I use. Except Cox 049's of course!