'65 C10 Short Step... I got one of those too!
As for my square body comment, the 1973 to 1987 Chevy trucks are a.k.a."Square Bodies":https://www.google.com/search?q=square+body&ie=utf-8&oe=utf-8&aq=t&rls=org.mozilla:en-US:official&client=firefox-a&channel=sb
Good to read you received the tank. I researched the 21 gallon Blazer style tanks when I installed a rear tank on my truck. Some folks find the blazer style tanks hang down to low, some folks think they are "just right". The reason folks notch the cross members is to try to tuck it up out of site as much as possible. This is especially critical if you don't run a rear bumper. The bumper will hide the blazer tank, some what.
Got any links to some photos of your truck?
