A couple winters ago I was needing a block heater for my '65 6X6 but all I could find was the automotive style with the flimsy spreader bar that that I refuse to use. Searching for other parts on ebay, I ran across this block heater.
Block heater.jpg
The instruction sheet shows the same block heater for a 3150/3160 Cat and V6 GMC.
A quick search reveals that ZeroStart makes an industrial style block heater for a 3150/3160 Cat!
Just thought I'd share as the Almanacs are forecasting another nasty winter...