How deep are the 3/8-16 holes in SBC heads? I need to drill and tap one that was never drilled on my passenger-side head.

 

You don't need to do that, it will hold up just fine w/o that extra mounting point

I did the same thing on my Blazer and never had any problems, just bolt it up and go.

 

I agree, that extra hole would be nice but not needed in my opinion. Just make sure, as I found out, that some of my bolts were bottoming out and were about 1/16" too long and I wasn't getting the bracket securely bolted to the block. Check depth and trim the bolts if needed.

 

I just figured since the other side has five mounting points, that having four on the tensioner side would be a good thing. I have to take the bracket back off and trim a bit of it to clear the compressor lines, anyway...figured I could use the bracket as a drill guide, then tap the head once the bracket is off.

 

Be careful when doing that. That aluminum is very soft and the bit spinning with any kind of lateral force will waller out that hole. I would use the bracket as the guide for a mark only, then pull off the bracket and drill the hole free hand.

I contemplated all this as well since the 350 heads in the car right now don't have that third hole.