I used a 21 gal side fill kit from one of the vendors, don’t recall which one, in my 66 c10 short stepside. I know several vendors sell it as I viewed a how to U-turned video from Brothers. Details are in my Project thread. FWIW, tank is said to be a Blazer unit. Thinking about it, I believe it came from CJ Pony.

1966 C-10 Short Stepside
HiPo
Step-by-step ~ and on-going resto build
in the Project Journals