Is this a rebuild or just a cam swap? I would use cam designed for a large truck with big tires...trucks weight upwards of 7~8K and with 35" tires they are dogs, a cam with wide LSA, high lift and short to moderate duration is what I did on my 78 powerwagon. Upping compressions to 9.5-10 to 1 would also help, longest runners on the intake you can get also makes a difference in your cruising experience. I saw someone in Idaho put a long ram intake on their 440 and it ran out of steam at about 4k rpms but was a beast up to that point. None of these options require a turbo or massive changes (except the intake) also a good tune and distributor curve matched to what rpms your engine is built to run. Tim