I’m a dummy it seems.
I replaced motor on my equinox. Has same trans as my vue. I have leftover 4” long bolt. I’m not done but for the life of me I can’t figure out where it goes. The ac compressor is bolted to block. Uses similar 4” long bolts. But only 3. I am sure. I’ve done lots of major work on cars. I don’t “misplace” stuff. It is something that is about 4” deep/thick. It’s not the bellhousing bolts. They are around 2” long. Alternator pivot bolt is in. That’s about 3.5” long. What can it be?

 

I don't have an Equinox, but I have just R&Red the manual transmission in my Ion to replace a blown slave cylinder. The aft transmission mount on it is bolted to the subframe with three long bolts. Not sure they are that heavy though. The front transmission mount bolts up with a single through bolt that may be that size.

 

Yes front trans mount is in. 1 long bolt for pivot/donut and 3 shorter bolts. New motor has alt bracket bolted to VC area and the bolt will not slide thru pivot On top so I don’t think it came from that area.

 

If that's a place where it looks like a bolt should go, check your alignment. It might just be a tad off and you need to loosen some of the other ones in order to get a little slack and line it up.