Just read through all 33pages, awesome work so far!
I did see some early attempts/work into making a kernel for read and writing for the ECUs.

I started looking through a kernel, but cannot see the registers for the DLCMD (Data Link Controller Module) where its actually reading or writing VPW frames.

From what I understand, these are using the HC11 processor.. and looking through the datasheet, I dont see a dedicated register for J1850 VPW communication, but I do see that in something like a HC12.
Is this all being doing using something like SPI? Anyone dived further into understanding that?