FYI - I have a 1970 Bronco, purchased it new in fall of 1969. The main stock fuel tank started rusting and gave the fuel filter fits until I had it cleaned out and coated at the local radiator shop - a few years later it started leaking, I then replaced it with a new metal tank (sometime in the 80's) only for the same thing to happen a few years later. I pulled the tank and found it was again coated with crud and rust, the sending unit was so rusted and coated I was amazed that it even worked. The auxilary stock tank (fiberglass) never had a problem of any kind and is still being used without leaking or clogging the filter, I pulled the sending unit from it, and it looks like new.
Long winded, but my point is buy a fiberglass tank - stay away from the metal one, it'll only give you grief later down the road. (My personal opinion, others may disagree however, probably if your going to do some real rock bashing, you may want a steel tank!!)

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