I have also been working with the sound insulating stuff.
Standardplast products work fine for me, nice pricing and easy application.
I put some Vibroplast on the fire wall's inside, plus the wheel wells.

I also did the rear seat area and rear wheel wells.

...and since I now wanted to do the trunk area too, I had to clean it up a bit:

And this is the end result:

A project of three years has changed some of my objectives a couple of times.
A while back I wanted to make this car almost 'full race', but now I'm after a more civilized result. That means I have started thinking more about the sound levels. I'm not building a stereo car - I'm not interested in that stuff at all, but I want the car to be easy on the ears on longer trips of which there will be many in the future.
So I also put some silicone seam filler on all the lateral seams on the inner roof:

That should help the vibration-induced noise from the roof area, without having to put on any heavy insulating stuff this high-up (would not be nice for weight distribution).
The aluminum-covered butyl sheets work best against low-frequency noise and vibrations, so something else was needed for high-frequency noise:

This adhesive-backed foam stuff is good for that, although stupidly expensive...
I covered all the seams with some special tape to help the seams not let unnecessery sound waves through, and also to stop the glue residue from sticking to the carpets later on:

It looks likely that this is the only piece of factory sound proofing that will stay in this car.
For the rest, I'm trying a kit supplied by VW Heritage UK.
So I will still have factory-style sound deadening mats on the floor, but under them a foam solution, under which there is the butyl mat. That should be quite enough, even though the factory "filler" style stuff has been removed from the floor.
I'll see how it works next spring I guess!