Jeremy, this looks like an F150 or F250 booster, the F350 booster is smaller in diameter but much fatter as there are two diaphragms in there. The good thing about the truck being a '79 vs. any older is that the brake booster pedal rod has a straight shot through the firewall (older models used some funky linkage), which will make it much easier for you to install a newer booster, be it hydraulic or vacuum. Also, I think your engine is from a van, judging by the location of the fuel filter. And I agree with pulling blocks from both the front and the rear, really you should not be running any more than 4" blocks in the rear and it looks like you have more than that now? Good thing about factory blocks is that they have ears for one of the U-bolts to pass through, so they cannot fly off like many aftermarket blocks can, I see at least two pairs of factory blocks on your truck so it will be a good idea to reuse one of those for the rear.