Id ask what power range are you looking for? You can drop in a f150 4.2 v6 itll bolt right up all u will need to do is slap on ur intakes.that will raise u about 25hp at the crank.
Cheap way you could run nitrous and keep the shot around 50-75 that run you 500 for the kit give or take a lilttle and a tune.
Or just build up a engine get a cam, ported head, ported intakes, a good full exhaust and UDP. that net you over 200rwhp +
My stock engine setup i ran a 11psi procharger in my 99 auto and made 278rwhp/274rwtrq .
My new setup ill have numbers after may 3rd when im retuned
For mods you can do true dual exhaust, underdrive pulleys, sct tuner, windstar intake swap, gears that should really make a difference. Then after that its port and polish heads and intake, cam.