Re: You could drop a 20V turbo motor in! ;) Otherwise, you'll never...
A 20valve turbo will run you in the neighborhood of $3000. Then figure in another couple thousand to cover the labor of the engine swap itself, not to mention any parts that need to be freshened up or replaced during the process. That'll leave you with 227 hp in a 2900 lb 80--not bad, and you can go up to 350hp reliably with that engine.
A cheaper option is to swap in a 10valve turbo, as I have in my '89 80q. These motors are plentiful, and a complete swap can be done for the cost of a 20valve motor alone. I've got around 230hp right now, and there's room to grow that figure to around 270 or so. Good luck.