Have you enquired at any local upholstery companies Guy,
I tried sourcing the lining once for a couple of mine and couldn’t find anywhere that supplied anything close
I do like Horace Andy, he still sounds great after all this time, I was only listening to this yesterday , it was recorded around 2006 with Robbie Shakespeare
I like the muted sound and I think I’ve got just about every mute you can buy, I’ve got a thread on them somewhere, but imo the foam does a great job especially on precisions with flats
With the degrees stamped on them they should be tapered, I’d say that’s their fault for sending spacers instead, let them know and hopefully they sort it for you