Continental C90-12F

Any 415C with a C90 at ERCO was experimental and won't help at all. That plane sounds like a paperwork nightmare. You are limited to what the type certificate says and it says C75 or C85. The only way to have another engine is with an STC, which does not exist for the 415C, or with a field approval, which is valid for that airplane only. The factory would not have done either, just registered the plane as experimental. Besides, I think there was only one Ercoupe on floats and it crashed.

There are plenty of STCs and 337s for D model Ercoupes. I know there are some C models flying around with O200s, and it seems to me an approved 337 for an O200 would qualify as existing data for getting one approved for the C90. But that might be assuming the FSDO person really understands how it all works. Some FSDOs now have a blanket "no field approvals" rule, while some are still amenable to the idea. It's like getting IRS audit - the rules aren't nearly as important as the person doing the auditing!

I'll dig through what I have to see if I can find something. You could also talk to your IA and see what he thinks about the chances for a field approval.

My 5-string one of the early Scruggs Standards. It's a funky color (baby poop yellow) and has the small peg head. I've been playing it since 1994 and I'm content with it. Which tone ring do you have? Archtop, ball bearing, flat head?