Welcome to the forum. Always glad to have another Subaru converstion.
Rear mounted radiator? Just ask Panelfantastic his opinion of a rear mounted radiator. Rob tried it too. I'm doing a front mounted radiator myself. I tried to hide it to where it's not as noticeable. The saying "Form Follows Function" applies here. Would you rather have a cool engine or the radiator in the back? You can put a radiator up front and make it tasteful. What kind of use do you want with the car? Daily driver, weekend warrior...? It would be rough to daily drive it with a radiator behind you, cuts down on space a bunch. If you mount it up front you can still have a rear seat.
You also brought up cars with rear mounted radiators. The fiero, from what I've heard, would have been better with a front mounted radiator. Still, the other cars with rear mounted radiators were designed and built for a rear mounted radiator. Our cars were not designed for a rear mounted radiator. It's not by any means impossible. Don't get me wrong, but it would be better to go with a proven set up, over something that has been tried before and didn't fly.
In my opinion you'll have to ditch the stock intercooler. You'd be better off with a air-air intercooler. Unless you want to cut up your package tray.
Adapter plate system? Mine is just a plate with a specially made flywheel. There are not any bearings. And I wouldn't worry about KEP products.
Don't worry about all the questions. That's why this thread is here. You might want to read through it if you havn't already. A lot of post, but a lot of good info too.