Sounds like that will be a good solid motor and I think 550 is very possible with 9-11psi on that motor.
Stock block will take a lot with a good tune, my buddy "MUSMONDO" had a 750RWHP XX-Trim 23psi set-up on his stock 89 block, shifted at 7400rpm and it lived and is still living in another car with the same set-up, it's all in the tune, he ran a DFI and had everything tuned in right. Although I still can't see how he did that.
Good Luck, now lets see how the tranny holds up
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[b]12.16 @ 113.5, 1.78 60ft..no traction in the 90 degree