You can buy a good used 420 engine for your car for as low as 500 bucks. Your conversion will run you closer to 10,000 by the time you are done. It is very difficult but has been done by a few.

If you want a hotrod, slap a Euro 500 or 560 engine in there and lower your rear end ratio (numeric rise). Way cheaper and more fun than putting a Chevy engine and transmission, and a Mustang suspension on the front of a 126.