Jonathan,
Welcome to this forum and the wonderful world of CMPs! You have taken on quite a challenge if you want to rebuild your truck back to C8A HUP configuration, but anything can be done of course. I would advise to start collecting information and parts and in the meantime use the CMP as-is.
There is a
spare C8A frame available here on MLU, maybe it's an idea to buy that and start building the body, and then transfer the mechanicals onto it once you finished the bodywork?
Anyway,
here's the link to the earlier thread on this truck on MLU plus the
for sale thread for the other members to see what you got.
Regards,
Hanno