When I built my first BB several years ago (a 289 casting) I drilled a cooling hole in the base of the deck to accomadate the hole in the FelPro gasket. When I did this I am quite sure I remember there being two existing holes and I added the third.

I now have a 512 casting and it only has one hole on the bottom of the deck. What do you guys do about these holes, do you drill them and does my memory serve me right and there is three holes in the FelPro performance gasket?

If I'm thinking of the same holes as you, drilling them won't make much difference unless you restrict water at the very back of the head, to force circulation through the "new" holes. Look at the difference between a Gen 5/6 gasket and a MK IV gasket at the large openings at the rear of the head--The MK IV has 2 large openings, the Gen 5/6 has only one.

I researched this when installing Gen 6 L-29 Vortec heads on my MK IV 454 boat motor.

The Gen 5/6 blocks and heads use the three extra holes. It is called "parallel" cooling, as opposed to standard MK IV "Series" coolant flow. Either way works, but in my opinion, parallel flow is somewhat better at reducing uneven coolant temps.

In the case of the L-29 heads on MK IV block, you could use the MK IV head gasket and no modifications, or the Gen 5/6 head gasket and drill the three holes in each deck surface. (In my case, drill 2 new holes, and oblong one existing hole to match the gasket on each side.)

Does the Gen V/VI gasket have the reduced hole size for proper water distribution? Are you using an OEM gasket or a performance gasket? Any p/n's handy. I want to run a gasket that's 0.039" compressed. Thanks.

I am crutching this engine through another season. The short block is a flat-top piston, stock cam POS. The pistons are .018-.025 down in the holes, so I used a pair of Mr. Gasket steel shims to put the quench distance close to correct. (I also like the idea that steel shim gaskets are cheap.)

The composite gasket I had as a reference was a Victor Reinz unit, stock style. Yes, the coolant circulation at the rear of the block is restricted. One passage is open, the other is totally blocked.