This gets discussed every so often.... hoping there's new (better!) info out there by now.
I haven't been able to find good quality, long lasting OEM-style rubber mats (with tails) for my high-hump '72 K20.
Last ones I bought about 6 years ago looked good at first, but lasted less than 4 years before cracking, splitting, & dry-rotting.
Has anyone found a mat that might be worth trying?