Engine swap conundrum

Hey guys, my 67 barracuda currently has a 440 in it, super low compression with a low lift/high duration cam and a tunnel ram with a pair of 600 holleys, 727 trans and 8 3/4 rear end with 4.10 gears on a spool. It is well tuned and is a super fun car to drive. I am going to be building the engine up, and I'm shooting for the 500-600hp range with some good heads, a real big roller cam, tall domed pistons and most likely fitech fuel injection. Now the dilemma is this: she's originally a formula S 383 car, and obviously the 440 isn't original, but the previous (and original) owner just found the original 383 engine in his barn and gave it to me. Will i be disappointed with the power difference between the 440 and 383 if i do the exact same things to each? And will having the original engine make a difference in the value of the car great enough to justify the swap? I might be over thinking it, but i figure you guys will know more than i do.