what can be done to a 454 420 hp to gain more hp and not break the bank ?

Make them 502's, and have I got a deal for you!

whats the deal?

Mark IV, change to a nice roller cam set up would be my first change. If the bank has the money to go deeper aluminum heads and some pistons to up the compression to around 9.5:1. You got a good basis to work with there.

I'm not sure what kind of gains your looking for but you could always get rid of the water circulating pump and go with a cross over. I'm not sure what the gains are but it won't break the bank.

it a 1979 454 420 hp motor with about 400 hrs would like to get to high 400 hp or 500 hp what cam would you suggest also heads and pistons

poke n stroke them .

Put a 174 blower on it and you have a hawk 525. Take about 3 hours and $1500.

does anything have to be done to motor to put blower on it or just bolt and go

If they run strong and are healthy right now, bolt on and go. Of course there will be an endless list of "should do's" but if there are no issues right now might as well make some
Jk the engines will be fine with a 174, or 250 blower.