Hi Mark,
Just posted the following on another forum.It is more directed at the restoration process;hope someone finds it useful.
I have made a new firewall insulation pad using a combination of 5mm felt-backed vinyl fixed to 5mm double sided foam sheet. It looks very close to the original and is constructed in the same manner (as the original) with the advantage of materials of superior quality, and is the thickness of the original, as most replacements I've seen are too thin.
My car is being restored so the firewall is stripped out, which appears essential if trying to make a template.in one piece.
Making a paper template against the metal firewall will not transpose onto the insulation and fit correctly, as the extra 10mm thickness of material layed over the curved firewall requires a larger surface area.
To make a template 10mm thick I used two sheets of 5mm thick bubble wrap.Use the transparent type.The firewall must have the old material removed. Tape the edge of a 5mm sheet against the edge of the upper drainage channel (bubble side down), and using a marker pen trace the shape and holes, cutouts ,etc, of the original insulation.Cut out unwanted bits.This is now the template for the first layer , the double sided foam sheet.
After cutting out the foam with the template(use sharp scissors),re-attach the template to the firewall. Now lay second sheet of bubble wrap over this, trace and cut out unwanted bits. This is now the template for the vinyl/felt material.
After the vinyl has been cut to shape,it can be glued to the rubber sheet with heat resistant contact glue.Put greaseproof paper between the glued surfaces to allow true alignment.Bring surfaces together by sliding out the paper,starting from one end,checking alignment as you go.
Your new insulation pad can now be fixed to firewall using the same contact glue. Use paper as before to ensure true alignment when fixing to car.
If you use the bulk uncut factory pad insulation, your template will be the outer (or second) bubble wrap template.
Good luck,
Mike.
Brooklet. NSW., Australia.
64 230 SL auto RHD (in bits).