When we got together at John's place to assemble his 261, we had gotten some misinformation about it. It was supposed to be a "1954" block with the high water pump, but it was apparently a replacement block- - - -high water pump position, which should have had the doweled upper bearings, but the main bores were machined like the later model engines with the locating tab at the side for the upper bearing shell. The block had a 1959 casting date! Of course, the main bearings we had on hand were for the earlier design- - - -"no bueno!". I simply did the "measure twice- - -cut once" procedure, and drilled the block for the dowel-anchored upper bearings! That style of bearing also uses shims between the cap and the block to set the oil clearance.
Jerry
