big block spool mount bolt size

Quick question guys, I am putting a 440 in my barracuda with the spool type motor mounts. I need to know what diameter the long bolts are that go through the mount and the k-frame. I believe the small block bolts are 1/2" dia x 5 1/2" long, are the big block ones also 1/2" or are they 9/16? I have a 9/16 drill bit that fits through the holw in the mount but it gets a bit tight and was wondering what is the right size.

Thanks!