451 Stroker counterweights???

It's not the oil pan rails. It's the main structure around the main webs. Some forged cranks have more of a tapered edge and they will only need minor grindong on the block to get the required room. No cast cranks will fit at all. Generally I used take off .200" from the counterweights. Now UI use Brandon's 440Source B wedge 3.75 crank. It's cheaper than the machining, is a better part, and is easier to internally balance.