The 534's were pretty popular up into the early 1970's, particularly in fire trucks. There were pretty reliable, made good power in the early years, and used a lot of fuel. I think the big Ford's were better than the International 549 V-8, maybe not quite as good as the G.M.C. 478 V-6 and 637 V-8. The Ford Super Duty's had a very unusual head design, similar to some of the early Mercury V-8's and Chevy 409's. The combustion chamber was in the block, the bottom of the head was completely flat, and the deck of the block was cut at an angle. I think the last year they made the 534 was 1981, and the last trucks that used them were the L-900's and the C-900's. They were very rare by then. I talked to a Ford engineer once about the Super Duty V-8's, and he told me that through out the 1970's, the 534 made less and less power due to the emission controls needed to clean it up (that head design was a problem). Ford got to the point that the 534 made about the same h.p. and torque as the 429 Lima truck engine, so they dumped it.