If you want to squeeze a big shot go with a 306 w completely forged internals. From what I have read and heard, 347's arent supposed to have any more than a 150 shot. And thats supposed to be pushin it. The 306 will be more durable and be able to take the abuse of the nitrous much better.
I am starting my own 347 project very soon as well. Im looking at all motor though, with high compression pistons and 58cc AFR heads. Good luck with yours and keep us informed
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95GT B303 cam, 1.7 rockers, 65mm TB, milled heads, 355's K&N, BBK Longtubes, Flowmaster cat back, pulleys, msd coil, 9mm wires, Tremec 3550, Pro5.0 shifter,10.5 Motorsport clutch, FMS aluminum driveshaft, weld in subframe connectors