Depends on the year of manufacture, but model no. is typically stamped (sometimes crudely) on a raised boss or other flat-ish surface near the bottom of the power head case, aka the "engine block".
Typical 40s-50s models would be "HD25", "TD15", TD20" etc. Two letters + two numbers is typical.
Unless there is a separate model / serial plaque, it’s going to be stamped directly into the case 99% of the time.
BTW – Howdy friends, old & new! I was totally flummoxed when I couldn’t find the forum.. just figured out what went on with the server loss, and got re-regged today!