I know that this 51 M has the Fire crater "power pack". Dad added this approximately 1961. He also at some point changed over to the vertical Delco distributor as he had a mounted corn picker and a loader. Vertical was easier to access. So presumably, the Delco would be restricted to 22 degrees advance - just not sure. The existing Delco is toast from sitting out. These vertical Delco distributors (and parts) are near impossible to source online and I am 2600 miles from any salvage yard local to the M. I am leaning toward just going back to the horizontal IH which is more available. At any rate, I will either keep the Fire Crater or install M&W or equivalent Power Seal stepped pistons so I will be needing a 22 degree advance. Pete 23 has talked about altering the hole in the 40 degree plate. I would maybe attempt to sleeve the boss on the cam sleeve instead. However, would it be just as well to get the 450 distributor 362473R91 - which has 25 degree advance?