Spanky,
The Holmes serial number info is:

Cat no. 515E
Serial no. TF7
Model no. 2335

Not sure if 2335 is the model number or the production number.

This GMC wrecker has a chassis ID of EC303, which makes it a 300 Series made in 1946 (from http://www.oldgmctrucks.com/page0016.html ).