Due to having a MGB that I am restoring I go onto this forum on a regular basis; https://www.mgexp.com/forum/mgb-and-gt-forum.1/   There are regular discussions about both heat and sound insulation, the heat insulation is not really relevant but the sound proofing is. The camp is divided in two groups, one say's that Dynamat is the ultimate product and nothing can better it. The other group say that Dynamat is nothing special just clever marketing, they use other butyl rubber pads that are slightly thicker and a lot of others use bitumen based products like the Bostick one. Back in the day MG themselves used bitumen based pads, my GT has them on the door skins and they are still intact forty six years later. I personally think that the push to butyl rubber is due to environmental concerns rather than it being a superior product.
These are still available to dampen vibration and to level the floor in MGB's 
https://www.ebay.co.uk/itm/325632543497?_trkparms=amclksrc%3DITM%26aid%3D1110006%26algo%3DHOMESPLICE.SIM%26ao%3D1%26asc%3D277105%2C276749%26meid%3D29b4692b495f48319f447c4aec358a8b%26pid%3D101875%26rk%3D2%26rkt%3D4%26sd%3D315864121555%26itm%3D325632543497%26pmt%3D1%26noa%3D0%26pg%3D2332490%26algv%3DSimVIDwebV3WithCPCExpansionEmbeddingSearchQueryRecall&_trksid=p2332490.c101875.m1851&itmprp=cksum%3A32563254349729b4692b495f48319f447c4aec358a8b%7Cenc%3AAQAJAAABEEK7FTfzsGw0VauxYyX1IOHjsuXJ1NPjVWebvOca%252BJbVzh3VqcrGnLFKHjKk2M42BtfNs8bK1jFneKBZqmubi3Lyx3Riq12idUYNq7TsB94Peew0lx0QOGmHeHYjyU7tR44IVH3xF0qaosz%252Fxja6%252FPvMdr1ZqRzUjIQ2Fd1lJMhPU60IjYh2rtDma2zzNmK0XkF9HV5FtH2JmL1o5pM8vcIN7QOvEvVJNE9o4nVj%252Fexyy8zbTLht1lt3oRM7qFK2KvNeWs%252BkVX%252FLivMOTYvRDlFGfKsQRrcAZkOqOzbki4XBYFaaoH4%252FbIVN3IBxe6%252F0QISSXenSyc%252FrsG1P8Ai3%252Fa%252BBNVj7fmQBGAwnlDe3tjoz%7Campid%3APL_CLK%7Cclp%3A2332490&itmmeta=01JCZBKQNJG4N2FJ3B83HE18BD
Incidentally the product that I linked to is available in widths up to a metre wide

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