Dealing in plastic models anything we can glue together works as good as are imagination says it does, but in the real world the problems I referred to are far more than too much power for the VW transaxle to handle. VW transaxles have been used in V8 powered kit cars, off road racing, and 9 second turbo VW drag cars without problems for years. My friend Jay with the turbo Subaru engine is running a Rancho built unit and has driven that car cross country twice.
The first problem is length, the VW mill fits up under the body while the Corvair sticks out a good foot. Most of us don't like that look.
Problem 2, laws require a fan belt guard on exposed engine, not easy on (or pretty on the Corvair)
Problem 3 is the weight and lack of a rear motor mount, this insures broken front motor mounts and nosecones, from stress not power. Look at the VW chassis and you can see this is not an easy fix.
Problem 4 is the backwards rotation of the Corvair engine. The "fliped ring gear" fix has the transmission running backwards to the way it was designed and has problems oiling everything properly. Also the pinion is now driving the ring gear on the coast side, not a good thing under load. Reversing the Corvair engine is done, the cams, oil pumps and such are available but not cheap.
Problem 5, adapting the starter motor. The Crown kit falls short here.
The only way to do the swap in my opinion is the Hadley "Transvair" kit, which solves most of the problems by installing a rear "cage" that has the rear mount included, and uses the Corvair transaxle.