New Member with Gas Tank Question

[Dually Don]

Hi everyone. This may be my first post, but I have been scouring the threads on here. What an awesome forum. This is what it's all about, people with a common interest/hobby helping each other.
Recently I ended up at the right place, right time. I managed to score a very fair deal on a 79 C30 Dually, Regular Cab, 454, Turbo 400, 4:10's, basically been in one family locally since new. Really a pretty solid truck. It was originally dark green inside and out, but somewhere along the line they painted it white.
Anyway, getting to my question, I could have sworn that I read on this forum that if you had dual gas tanks that they would have been the 16 gallon ones. I laid under the truck today and measured the length and they're about 52" long. Were the one tons the exception to the rule? Was it pretty common on these camper specials to get a pair of 20 gallon tanks?
Thanks in advance....

Don