340 parts interchange & performance Q

Just wondering if any one knows what the interchange is between a '73 340 and the older ones ( '68-'70ish )? I want to breath new life into my 340 and let it live up to the CID reputation it was origanaly born with in '68. I'm getting a set of rods, pistons, bearings and windage tray from a member here and thought that I might have a problem with the internal vs external balance change over... I don't remember when they changed over and if it effects my '73 340 or not. My engine is a '73 340 block cast 8/8/72, every thing on the bottom end is stock ( even the stock bore ).
My plans with this engine are: I'm going with '69 pistons (to help the CR), change the "cleaned" up 360 heads to a set of mildly ported X or J heads (2.02's), Edelbrock performer intake (already cleaned up), performer cam & lifters, I want to use zero gap rings, and a double roller timeing chain. If I run across one that I can afford I'll use a stock forged crank. Any one have any input on this combo... what it'll put out and any sugestions?
I already have the cam& lifters, intake, timing chain, will be getting the pistons, rods, and windage tray soon ( from a '69 340 ). This is just a back burner budget build that I don't have anything to put into yet.