Transmission crossmember bolt sizes?

The later crossmembers had a funky 3/8 bolt with a tapered 1/2 shoulder under the head.
OK, that explains it then. The only reason I can imagine they did that was to make sure the bolts were inserted the correct direction. I don't know for sure which way they're supposed to go in, but the bolt heads should be closer to the rear, threads towards the engine?