4 x 4 and 2 x 4eng mounts are totally different from one another.
what you are describing in yours sounds correct. some of the later perches will mount in their place to takke the later insulator( the one that has the horizontal bolt running through it.
perhaps this link will help you, http://www.speedwaymotors.com/LS1-Motor-Mount-Adaptors,5070.html.
if not check some of the aftermarket shops as most will have something.
http://advanceadapters.com/product/3961/(P/N-713088-P).html
ron
BINGO! I just discovered the same. The 2WD brackets are correct on my truck. I just don't understand how I pulled a 350 out of the truck, but the new 383 won't drop right in. It is oh so close. I just can't line up the one side when I try to put the bolt through the bracket into the rubber motor mount. It's like I need a 10 ton press to push the engine farther down between the brackets. I guess I'll have to notch the holes in the brackets so they spread wider apart.
