55.2-59 Sound Deadener and Vintage Air

[57FleetsideC4]

Hi All, I am to the point on my 57 truck project that I am putting down sound deadener on the floor and firewall and have a couple questions. I am using Fat Mat on the floor and firewall up to the cowl and would like to know if this stuff will stick to the bottom of the cowl? I would also like to know if it is worth putting the 1/8" dynaliner on the firewall? My Vintage Air question is for anyone who has installed a Gen 4 system on 55-57 how tight of a fit is it behind the dash? They say to cut the original firewall pad where it bolts to the firewall. I don't have a the original pad in there just the .050 fatmat but if I put the 1/8" dynaliner there will it be to tight? Thank You Steve