5.9 Mag stock LB or rebuilt SB
What cam is in the rebuilt?
? I’d like to get to 400 hp and this will be a street only car, no racing.
Yes you can get to 400 with a 9/1 Magnum but the power will be a good 400rpm higher than with a 10.5 or 11/1, and that means a cam one or two sizes bigger, which will move the torque up off the bottom end, requiring a higher stall convertor, and a rear end swap to at least the next size bigger. Add up the costs of the convertor and gears, the extra cost of fuel from the loss of fuel mileage, and your gonna get to the cost of the piston swap pretty quick.
and I gotta tell ya, once you drive a car with 190 psi cylinder pressure, you'll never go back to 155
In fact, if or when, actually, you do that, you won't need a big cam and you'll forget all about that 400 hp target. 300 is more than enough for that Dart. and such an engine will pull gears down to 2.94s, so you could be looking at sipping gas at hiway speeds. Couple that with an overdrive, the right cam and tune, and your 5.9/360 could be knocking on high 20s mpgs.
So, that said, I say build your own hi-compression engine with a small cam, a 2800ish TC, an overdrive, whatever gears will get you to about 60 mph at the top of second gear, probably 3.91s, and don't forget the posi and slapper bars; and who cares about how much power she's making, you'll be smiling no grinning like a kid after his first sexual encounter, every time the secondaries open. Oh, yeah, for full effect, put a spreadbore carb on it with tiny primaries and sewer-pipe secondaries.
Ok so; knowing what I now know, that's what I would do. and
BTW, to run 190 psi, yur gonna need to run alloy heads and a zero-deck, so there is that to think about.
Yes I'm spending your money, but, my way, you'll only spend it once.