Re:Which rivet tool is needed for P-30 truck build. Monobolt? Price range of tool?
Chevrolet P30 denotes a bare chassis, the body was made by a variety of coach builders. Your body may have been made by Workhorse or Grumann or etc. A few bodies/complete stepvans were made entirely by General Motors, I happen to have one--the thing does not have a single rivet anywhere, only spot welds and these annoying "clutch bolts" which were apparently only used on stepvans and Corvettes (!).
IOW your fasteners will depend on your coach builder, we can't help you without more information.