Do you have some pics of what you are starting with, generally you turn a 440 into a super bee or a 500 into an RT (the whole tail section difference). Either way a nice car..
I would find a big block k frame , they are plentiful, and depending on what you car has already that is usable, you need a big block radiator, tranny, maybe a nice posi rear end, either a power bulge or ram air hood, a rallye dash if you want to go that far with it, etc..
Show us some pics, lets talk budget and go from there...
Personally I would turn it into a pro touring car, they are worth more than clones (and some originals), the 440's are perfect candidates for the change, they drive better, etc...
Sell the 440, get a nice 340 or 360, build it fuel injected for around 425 hp, add some nice disk brakes, larger wheels with meaty tires, air conditioning, digital gauges, nice stereo, and a cool updated color...