I don't know $3000 would still be limiting a 340 I think? Unless you already had some really good X orJ heads laying with the 340 block.
The smaller 5.2 magnum needs less head . And responds great to bolt on mods. Heck do a $3000 forced induction setup on a 5.2 magnum and see 400hp with the right valve springs
Why only 400? Engine masters got 600 out of a chevy 305, with a monster nitrous setup. $2000 in a 318, make 300hp n.a. and hit it with a 200 shot? Easy mid elevens in a decent car.
Still under $3000.