If you get the metal clean, brazing the tank should not be a problem. In contrast to brazing, you can also consider using Harris Stay-Brite silver bearing solder and the acid flux they sell for use with it. It melts at a much lower temperature (450 F) than a brazing rod and can be easily used with a common Mapp or propane hand held torch. And this solder will bond to almost all metals (except aluminum and some stainless...nothing you'll have to worry about with that tank, however). Are these what you'd call pin-holes or are any of them larger?

~ Jon
1952 1/2 ton with 1959 235 | T5 with 3.07 rear end