A '74 will be a divorced transfer case truck and originally has one fo the heaviest drivetrains ever put in a 1/2 ton. The fact that they swapped out the axles is a bit of a minus in my book since all you gained was a more troublesome rear axle and disc brakes up front. I'd see if he still has the 8 3/4" and drum brake D44 that came out of it. The 8 3/4" is a much better rear axle in my opinion and the disc brakes can be swapped onto the old D44 housing to get rid of the CAD axle since it's completely unnecessary in that truck. Other than those issues, make sure the driveshaft between the transmission and transfer case is tight and the yokes don't have any slack. Check the floors, wheelwells, lower fenders, rocker panels, cab corners and the drip rail above the windshield for rust or evidence of crappy rust repairs. Like Dodgeboys said above, it's probably the factory block in the rear and the early '70s trucks sat up quite a bit higher on the suspension than the later trucks. If the truck appears solid and the price is right, I'd pick it up. My '74 W100 and W200 were two of the best trucks I have ever owned.