Magnum 360 build. (HP/tq?)

Do you have a part number for the pistons? The compression ratio given by piston manufacturers is based on a lot of assumptions. You need cylinder head chamber volume, head gasket thickness and bore diameter, and distance below deck when the pistons are at TDC to get an accurate compression ratio.

I think that cam will work great in a heavier truck application but I doubt your peak HP will be much over 400. It'll pull like a beast from right off idle though, very flat torque curve. I'd kind of hope your actual static compression is more in the 9.5:1 range as that'll be making quite a bit of cylinder pressure in the lower revs and it'll be under a good amount of load moving that truck around. 4.10 gears were definitely a good choice. I'd also run a 180-degree thermostat and a proper cold-air intake, NOT an open-element air cleaner! lol. Premium fuel will be a necessity. It'll have EFI right? Electronic ignition timing control as well, I hope?