2.6 Kenne's make good power, so like you said you'll need to forge the shortblock to handle the boost. If you're gonna make anything over 650ish I would advise stepping up to a full fuel system.
Glenns makes some real nice kits:
http://www.glennsperformance.com/index.php?cPath=24 They are expensive lol.
If you're gonna keep the boost to a minumum and push 5-600 ponies, you can upgrade to a Walbro 255 pump, 40 amp boost a pump, and some 60# injectors and you should be just fine. I know of a few people personally that push over 600 to the ground with that exact setup.
As far as a forged motor, I personally have an MMR 1100. The only reason I have it is because I got a really good deal on a used one, otherwise they're over $3k new. But if you have the bucks, DSS and MMR both make solid shortblocks. Otherwise just buy the forged internals separately and save money.