Thank-you Rich and Paul for your swift replies.
Ah! My issue was that I wasn't using the correct config, so I should've been using the v7 for my RPi board. And, interestingly, in that directory, the linux source file was named with the correct kernel version, so I think it was just a typo in the v6.
NB: The drivers I was seeking are to get 3D acceleration working on x windows. I don't see an extension for that, but I do see the drivers in the modules-5.4.51-piCore.tar.xz, so I can use those. I got this working on TC 11.0 and it saves a lot of processing for CPU if you're doing much OpenGL stuff. If there's interest for this, I could wrap my work into an extension - basically ko files and a couple of config files.