Just found part numbers on GMWIKI. Chevy truck and GMC both used this case.
Attachments
HT Chevy Tk.jpg (40.8 KB, 89 downloads)
HT GMC.jpg (46.77 KB, 88 downloads)


"Adding CFM to a truck will only help at engine speeds you don't want to use."
"I found there was nothing to gain beyond 400 CFM."