L92 heads FTW, you have a 4.0 bore so you can use them. Stock crank is a beast (casting # should be 12552216) and has proven itself in 1000 HP engines. I have NEVER heard of a crank failure. I'd get some H-beam rods and forged pistons and you should be good.
Having given it some thought I'd go with L92 heads and the L92/LS7 Carb manifold $2700.00 for the entire top end conversion and electronics or piece it out if you want to re-use some of your stuff. Only thing you couldn't use for sure are the intake rockers, L92 has offset
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