The blocks with the big gallery drilled for hydraulic lifters are probably the ones that need the lifters with the stepped-down center. The block we were dealing with on John's project was cast in 1959, according to the codes on the block, but it was a high water pump replacement block for 1954/early 55 engines, apparently, for the early 261 design engines. It still had the rocker feed line from the rear cam bearing area under the pushrod cover. I'm guessing that the later casting style with the low water pump might have included the different oil passages as well, and would need the stepped-down lifters. John's block was also machined for the later style main bearings. Since I had ordered the early style bearings with the dowel in the upper shell based on the "high water pump" situation, we ended up modifying the block so it could accept either type bearing. If I had been present for the disassembly, I might have picked up on the difference, but I was 700 miles away at the time.
Jerry
