getting ready to install my 406 SBC and noticed there is no threaded hole where pivot ball boss is on block. I have the 1/2" tap but not sure what size to drill hole as far as I can see it looks like 29/64" drill bit should do it but not sure. Anybody done this before please let me know so I can go buy correct drill bit. thanks Edd

Edd,
I had to drill my 400 block also,the boss was there but not drilled or tapped.I measured the threads on the pivot ball and then added an 1/8th so the threads wouldn't bottom out.One other thing you'll need a starting tap and a bottoming tap.
On the drill bit the closest I could find was a 27/64 so thats what I used,but the best advise is to use the size listed on the starting tap.

John thanks I checked on a chart for 1/2 coarse thread and it does say use 27/64 my taps are so old they don't have any info on them. thanks again and I'm going to start drilling in a few minutes

Scoggin Dicky sells a bracket that bolts to the bellhousing bolts and is used as a pivot ball. works great...and that way you don't have to drill your block.

drilled the block with 27/64" bit and tapped it with 1/2" coarse used some thread loc and it all fits nice ---- thanks guys and thanks for the heads up on the one that fits on bellhousing may need it sometime.