85 to 73 Cab/Front Clip Swap

[softballnrd27]

There are a few reasons why I'm doing the swap:
1. My cab has some rust issues in spots that I don't feel comfortable fixing
2. The donor cab has no rust issues.
3. Mines and 85 and I'm required to have the emissions system in place.
4. I'm getting the whole truck for a really good price and I want the 73 front end and no emissions

Now my plan is to:
Gut the cab get rid of the A/C, patch the holes from the old unit(Vintage Air in future)
Swap the body mounts
New Mounting hardware(Poly or rubber?)
Swap over most of my interior
What is a cheap but good insulator/sound deadener for the floor?
Is there any advice or things you would/wouldn't do?