No block mods are needed for a 505 as long as you follow the plan laid out above. 4.250 crank with Chevy 2.200 rod journals. Then you use 7.100 long BB Chevy rods and a matching piston. If you buy the correct parts it goes together very easily. Stock oil pans clear, a windage tray will clear, the stock oil pump pickup will clear. If you stray off the path then you might have clearance issues.