build vs crate

[Berg]

I feel it all comes down to how much machine work you'd have to do- that's where a lot of the cost will be. You could also do a poor man's head swap and run the 100CC Gen 6 Vortec heads on you Mark IV 454 with dished or flat-top pistons. If you are in the neighborhood of 7.0:1 or 7.5:1 I'm going to venture to guess you have dished pistons. In this case, doing the head swap should put you around 9:1 and combined with a healthy camshaft and a nice intake and carb with HEI ignition I think you'd have a pretty powerful combo that would be totally streetable.
There is also the benefit of having a nice warranty that comes with a crate engine. Personally, I like the 454 HO crate engine from GMPP. Kind of hard to beat that deal!