Carb Mounting Bolt Holes Through Manifold?

[12784563]

As I'm continuing to clean up the engine on my comatose '62 401 nailhead, the parts cleaning brush just whisked off the head of the carb mounting bolt on the front passenger side of the carb. Apparently, some Mr. Badwrench did a little torque-too-much on that puppy and when she got elastic, finally pulled the wrench off.

My question is: Do the carb mounting bolt holes go clear through the intake mainfold or do they bottom out? I hate to start drilling this guy out to find that I have littered the interior of the manifold with drill shavings.

Thanks

[BuickStreet]

I have a 401 and looking into the engine bay at the motor, the right hand bolt on the front of the carb stops but the left hand front (or passenger side for those in the US) just keeps on screwing into the manifold. I use studs on all four corners and the two rear bolt holes seem blind as well. So, I'd say that three are blind but one is open.