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for the record, you could do a LS6 383 or an iron 408 with no wiring changes whatsoever. If you went with a 416 LS3 block, the wiring changes would be inexpensive and minimal. Relocate the knock sensors and cam sensor. 50 bucks in parts and the actual work is a joke. I would not hesitate to upgrade. Your car will make a ton more power and sell for more when you decide to sell it.
Here's the 383 shortblock from GMparts dealer, Scoggin and Dickey for 3949.00/ The 383 will have a forged crank, H beam rods and forged pistons.