kdub,

The Hyster serial number should be something like this, P007V01573R. Letter, 3 numbers, letter then 5 numbers finally a letter. If the C5D9831R is part of the serial number, suspect the year is 1971. Not sure without a picture. Remove floor plate and look at frame for serial number stamped into metal frame. The Chrysler 227 slant 6 was used in multiple lifts from 5000 pound to 8000 pound capacity. Good Luck