I used 1 layer of foil backed butyl rubber with peel and stick for sound deadening (it is in the roof section at Home Depot) costs about $1.25 per square ft. This holds the noise down.

Then I went back to Home Depot and bought a simalarly built foam insulation (used for A/C Ducts--has alum one side, foam on the other, sticky on the foam side....$1.25 per sq ft...

So for $2.50 per sq ft I sound deadened the front firewall floor and rear of the cab on my 66, and insulated it also. at 80 with the windows down you can carry on a conversation and you get no heat from the engine.....today I am driving it with no A/c the only heat is from the sun.......Kieth

We used silver tape to close the seams:

http://kieth.smugmug.com/Trucks/66-GMC/13311086_gRF57#1335223625_3HTCKCG-A-LB

http://kieth.smugmug.com/Trucks/66-GMC/13311086_gRF57#1335224042_w3P4ST2-A-LB

http://kieth.smugmug.com/Trucks/66-GMC/13311086_gRF57#1249354752_U7LmV

since we could not leave the floor stock we ordered a full cab floor mat from Raybuck.com then put the stock floor mat over that so it looks quasi stock, is quiet, does not transmit heat, and is easy to keep clean.

http://kieth.smugmug.com/Trucks/66-GMC/13311086_gRF57#1438205324_TJ6s3L4-XL-LB

http://kieth.smugmug.com/Trucks/66-GMC/13311086_gRF57#1438205345_QRXTmdg-X2-LB

I think the full rubber mat cost $135.00 plus shipping Kieth

66 GMC SWB
65 Chevy LWB
65 GMC SWB

918-446-2245