[84LX89GT]

a 351 windsor engine is probably one of the easier swaps with good results from the increased displacement and swap components. a 4 cyl. mustang is a good way to start since they are plentiful and cheap, if you want something more more rigid and lighter a notchback mustang (with trunk) is great for drag racing and the frame twists less than a hatch, a convertible is not the best choice for a drag car, but is great to cruise around in the sun with although the chassis would need to be beefed up especially with more horsepower.
I'm putting a 400 modified in my '85 LX, which is a weird and harder swap, although so far it's been VERY cheap - but i don't have it all together yet.
Another fun project is a 460 into a mustang, although easier than a 400 351m, it can be cheap if done correctly.
Finding used 302 engines is another option since they are readily available and stock parts can be used for a swap.
Have fun!