IMO if you have the Dynamat down already then there is no need for the factory tar matts.

I used an equivalent product and still had heat coming through the floors with the big 455 and 2.5 X cross over exhaust.

So I would either throw a layer of Jute, a thermotech blanket or a sheet of foam over the top before carpet. I found a roll of 1/4 foam at Sears that is meant to go under a treadmill that I might try for one of my cars.