Yes Bill, the in-cowl bolt pattern is the the same for both Evolution .61NX-NT, O.S. 61FX and O.S. 91FX. However, they discontinued the Evolution In-Cowl Muffler at the same time they discontinued the Fokker DVII. You might find one at E-bay or RCU Market place once in a while and might find one at a swap meet. I think Bisson also makes a 60-90 in-cowl upright? That might work.
So your better off not using any of your .60-.61 2-strokes in my opinion unless you use another muffler, you might have to do a little modification to make it work if you use any other muffler of that type that isn't stock made for the 60 Hanger 9 Fokker DVII. (ie Evolution In Cowl Muffler)
Most people used the 4-strokes for theirs anyway. Just a handful including myself stuck to the recommended Evolution.61NX engine. Some switched to O.S. after I did and noticed a big difference. The O.S. is a little heavier, more powerful and runs cooler in any in cowl situation, plus their life expectancy is longer.
Evolutions are built cheap and don't last very long. Me personally I don't like the needle design or set up. I guess I'm spoiled by O.S. and Saito. I've had nothing but problems with Evolution and I had 3 of them, so I feel I'm entitled to express my opinion about them. I owned a 46NT, a .46NX and the 61NT. I made key chains out of the pistons and chucked the rest of the engines in the trash. I had nothing but fuel leaks, the low end needle wouldn't stay put and I had gasket air leaks. One over heated and all didn't have the kind of power O.S. does of the same size. It's true in my opinion, that we get what we pay for. Besides, I don't believe in putting a cheap engine in a expensive plane anymore- to me it's just plain common sense.
If you want to do some light reading on the 60 Hanger 9 Fokker DVII I linked you the build thread. The thread is very insightful, and we not only talk about the problems we had with this ARF, but what we did to correct it. We also show how to do a few details to enhance the model for flight and appearance.
My avitar when I joined the build thread was "Luftwaffe Oberst" then later on I changed it to "Oberst." We wrote about the issue with the Evolution Engine and what we did to modify a few things here and there.
http://www.rcuniverse.com/forum/m_70..._1/key_/tm.htm
Wow, your engine is as old as my 1983 O.S. FS120- Before Surpass! (looks like a Saito) I took my 120 to my club meeting to show that I rebuilt the engine. Only a few "Ol-timers" knew what the engine was. One guy (A Korea War Vet) came up to me and he said he had 4 of them!
I told him to keep them because they go for up to $250.00 used on E-bay. I looked up my O.S. FS91 Surpass II, usually they go up to $350.00-$400.00 new in the box. ( If you can find one)
Used like new $200.00-$250.00. I bought mine for $150.00 from a E-bay Quikdrop from Florida. I noticed that the high end needle was taken out and the spring bent, the owner didn't say why- but he did however tell the store that it runs. I'll go through everything and make sure she has good compression, I'll check the valves, rocker arms and check for carb barrel play etc. All parts except for the casing is still on the market at Tower Hobbies, so I'm figuring it's still a very popular engine. Not sure what year it was introduced, and when it was discontinued, I'll have to look that up.
The questions I have is when do we stop using the classic engines? When we can no longer get any stock or cross reference parts? Or when a carb or parts becomes $100 or over to replace? Those question has not been answered yet, and probably won't.
I've rebuilt glow engines before, but kind of new to collecting them. There's a nostalgia about the hobby when we hold a classic or antique engine in our hands. I start thinking about its rich history, and how many owners had the engine before me etc. I caught the bug!
I know, I'm a little weird- I can't help it.
Pete