Ran the truck yesterday -- it appears the issue is fixed. Compression, timing and gap all checked out right in spec. Jimmy rebuilt the carburetor and, in the process, removed a goodly amount of mechanical pump diaphram bits out of the high speed jet -- amazing that enough pieces made it through the stone filter to be a problem like that.
Freshly rebuilt carb, new mechanical pump (keeping the new electrical one in line as a standby) and she seems as right as rain.
Winchester Fire Parade, here we come!

John
Thanks for all the advice and guidance!