727 Trans to 1995 360 Bolt?

Hey guys,

I was going to bolt up the 727 to a 1995 360 (I think its a magnum block) the other day and I was using 3/8" bolts and it seemed as if they did not want to thread. Am I usung the right size and thread pitch bolt? Anyone know the size off hand? These components were never together before its a new build so i dont have any "original" parts. Its not metric is it?

Thanks in advance,
Brian