The "max advance" has the final word on how much spark advance can be commanded by the ecm. Your total timing won't be more than max advance plus the "base timing" setting of the distributor.

The manual trans equipped trucks used a C3 ECM (not PCM) number 16196395. There is no manual trans + V8 pickup with a 7427. I've got some cal #'s from S10's using manual trannies but they're listed under different pcm#'s so I'll have to do more research when I can keep my eyes open.