seen them spit thru head bolt holes on a 040 over better start with a good block first . still alot of spacing thick spacer and thick bearing? upper spacers and small steel caps is the best way if you must use a 400 block with small SBC mains .still need a seal that can be made up . still would do a fill on the block but i not the builder i could make it work but when all said and done. i think your better off with a SHP dart block