And as mentioned that all 427's and 406's were crossbolted... only a few at best of 406's were factory crossbolted. These were 63 406's that ran in NASCAR and prototype for the 427 to come. Some 406's have the crossbolt bosses but have 2 bolt maincaps others have no bosses at all. With only a year in production (62 1/2- 63 1/2) the 406 was the tweener from the 390HP to the 427 with some unique things from both. Kind of a practice block it seems. I know this is about sideoilers but I'm an advid 406 guy here. For the sideoiler you also look for the "8" shaped
oil galley and
oil pressure releif valve at the rear of the block lower left side. G.