427 Chevy Block 2 bolt vs 4 bolt

[Rumbleguts396]

Originally Posted by rszmjt

I have converted 2 bolt "512" & "351" blocks to 4 bolt caps before for restorations, its not that hard to do just time consuming , it helps to have a good supply of used 4 bolt caps to trial fit on the block to make sure the parting lines are very very close, unless you have someone weld up the cap registers and re machine to center the caps on existing bore. Check with local machine shops to see if they have a supply of used 4 bolt caps to trial fit onto the block. Also the rear cap seal parting line area should be super close to avoid any rear seal alignment issues. Once you find some suitable caps you have to put the block on a mill or bed type drill press and drill & tap the outer bolt holes. I made a thin drill sleeve and used the outer cap holes to drill the block and used the caps as a tapping guide.
Then the block needs to be align honed ( if caps are super close) or possibly line bored. If you want block to look correct from the outside the 1/2" pipe thread 2 bolt oil plug above the oil filter must be tapped to the 4 bolt 3/4" pipe plug. It is a lot of work and can get expensive if you have to get someone to do the mill work and align hone or bore.

Hope that Helps.
Mike.

Thanks Mike much appreciated!!!