Go big now,505,511 or 512 C.I., and not have to wish you had done it later
On the camshaft look at Comp Cams grind #s 270H,XE268H and 275DEH.
Any of those three should put a big grin on your face from idle to a 35 MPH roll to shred those big tires with that pump gas stroker motor in that pickup Make sure to degree the cam in from 3 to 6 degrees advanced like Comp recommends, they suggest 4 degrees advance but 3 to 6 degrees advanced will work well, especially with the larger stroke
Last thing, first thing before starting any machine work, is to make sure and have your block sonic tested and magnaflux checked for cracks before boring it One of the first 400 stroker motors I assembled had very thin cylinder walls on the driver side of the block on the cam side due to massive core shift on that block, it cracked the #1 cylinder wall on the dyno and was not repairable