Bob,
I had a Jett90 bse here I was going to put in it. I had already cut the cowl and engine mount for the OS50 and discovered it was not heavy enough, plenty of power for 100 MPH +, just very light.
I laid the 90 up there and discovered I would have to cut the cowl even more because needle valve and muffler and carb locations varied from the OS.
This plane should be able to handle the 90. It weighs just a little more than the OS50 (not incl mufflers.)
In fact If you could add shims to the muffler to get it to clear and then use the Toni angled shim it might even be a cleaner fit than the OS. I think I was using a 10x6 on mine with all those shims I used on my Dago Red from World Models.
Take a look (I'm sure you have already) inside firewall area and note the lack of any reinforcement-it is straight wood former to f/glass fuse. Adding stock here for the 90 is a must. The wings dont look like they could handle a lot of repetitious turns under heavy loads. Maybe the 90 might push it to the limit there. Adding a glass section to center or even glassing entire wing would be the best overall solution for LONG term turning.
I had a Jett 90 in my World Models Dago Red and it lasted over 100 flights of pylon turning.
But their wing and engine areas were more structurally fit.
If I can get a new cowl I will drop in my Jett90 BSE and look up a radar gun and see what the top speeds will be. Maybe I will look up Mark and see if glow can out run electric power!!!
The 90 should push it to 125-135 for sure. Problem is it might push it too hard and fold in the corners.
Get r done Bob and let us know. I will check on a new cowl and wait for your report.