motor mounts for a '72 firebird?

[revhead]

I'm sure I'm beating a dead horse here, and I've searched, googled and whatever else but haven't found the exact answer i'm looking for.

I recently sold a project so now I'm trying to get back to my LS1/72 firebird.

I bought mounting plates like these:
http://static.atechmotorsports.com/g...edl-6701_w.jpg

Here's my subframe




And I bought a pair of new clamshell mounts that i see most people suggest instead of the stands and early big block mounts. Obviously I am missing a part to make this work. I guess it would be the big metal shell that mounts to the motor. I also have Engine mounting brackets that have a rib on the back and will not sit flat on the adapter plate.
so where did I go wrong?

Should I buy a pair of these: (http://www.rickscamaros.com/index.ph...s-_-718893-_-X) and hope they don't have the rib facing backwards?
or use the earlier mounts and buy the frame stand offs?