Jonsered engines are a class act.
I understood that they were built by Husqvarna and were an up scale version on the standard Husky..

The lower grade engines had plastic lower cases, as did a few other brands.

It looks easy to convert. I say go for it.

One thing I would do is get a set of rings from frank bowman.

ringmaster46msn.com

If you sent him the cylinder and piston you would end up with a "perfect Fit"
Yes I believe franks ring are worth getting and the cost is very reasonable.

By the way, because it is a chain saw engine you will not need to do any port work.
The porting on saw engines are just about perfect for airplane use.

What are the numbers on the bearings? NO use paying more than you have to.