340 Cam

With what you have, and please correct were inaccurate:

stock bottom end 340 (10.5:1 would've been 68-71)
M1 intake
2500 stall
4.10 gears
stock size wheels and tires (14x5.5??)

OK, you likely already have issues with traction...but I'll humor you a little...assuming a stock cammed high compression 340, and no other mods than an M1 intake, you really are a little limited by the valve springs and the age of those parts...so I'll say maybe a smaller split patter MP purple cam, a COMP 270 magnum, or one of the Summit cams.

we really need some more info to make a decent recommendation...