Is there anything wrong with the originals? Bad threads? bunged up seats? cracked? Those parts really don't wear, and should be reusable after a good cleaning. The one that these trucks use is also somewhat specific to application, as the mounting stud is part of the the T. If you do need to replace it, it is most likley 3/16" line, standard double flare. Very common. Some trucks do use 1/4" line, but that seems to be mostly 3/4 ton ans larger, along with the 3200 1/2 tons after '55. You should not need any adapters.
