Note that the 8-bolt block may have different bolt sizes on the main and bellhousing bolts.
The 6-bolt block has ½"-13UNC maincap bolts. The 8-bolt block I had used M12-1.75 bolts in both maincaps and bellhousing.
The 6-bolt block mounts the bellhousing with 7-16"-14UNC bolts.
DANGER! These bolts screw easily into an M12-1.75 tapped hole but have very little strength in the threaded joint. What you have is a 0.4375"-14 bolt going into a 0.475"-13.9 hole. Because of the difference in size, the pitch difference is so small the bolt goes in easily but has only about 50% thread engagement at the crests of the threads, and since there IS a difference in pitch, only a few of the threads are engaged at any time. Therefore you will be stripping only one or two threads at a time if you attempt to torque a 7/16" bolt in an M12 hole, and it will strip right out.
So be SURE what threads you have in a bolt hole - if it screws in loosely or way too easily, better check again!

Another trap is 5/16" (0.3125) vs M8 (0.315"). But here you can't screw them together easily because the 5/16" bolt will have either 18(UNC) or 24(UNF) threads per inch while the M8-1.25 bolt has approximately 20 threads per inch.
I can usually tell them apart visually after a number of years' experience.
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George Downs Bartlesville, Oklahoma