More info is needed. I'm assuming now that you're talking about your rear brakes on the 2-ton, which do have adjusters separate from the wheel cylinders, but your front brakes would be single cylinders with adjusters on the ends of the cylinders. I found the picture in the service manual showing a picture of the rear brake assembly with the separate adjusters. Here's a
Link to Figure 3 in the 47-51 Truck Shop Manual. The '52 supplement has essentially the same figure of the 2-ton rear brakes only bigger, so your '51 should be the same.
So, I'd say heat away. I'd use PB blaster and heat alternately to free up the threads on the adjusters.
BTW, from looking at the manual, it looks like your 2-ton has Huck brakes and the rear brakes are called "Twinplex" which were manufactured by Bendix.
HERE is a website I found detailing those.
HERE is a link to the adjustment procedure, with a clearer picture of what you're dealing with (Fig. 26)
