[bilfman]

You can probably resurect the old tank. Keep in mind it will for sure be rusty. I would suggest putting 2 inline fuel filters right out of the tank. The the dirty gas will be filtered twice before entering your system ie pump, switch and existing filters.

My guess would be the biggest issue may be that your tank switching servo may not work. It is easy to replace and it is back by the right hand fuel tank.

So easiest method would be fill up that tank to minimize rust to gas ratio, see if tanks change, easy to see by fuel gauge, if gauge changes and fuel goes down after using it a while, the switch and servo are working. Just be sure to stuff at least one filter in right out of the tank and be prepared to change these a few times. At 4 bucks a piece its cheap insurance. Good luck.
The above is the hillbilly method and has worked fine for me in the past.

If you want to go all out you can remove the tank, remove the sending unit plate, throw a bunch of old nuts on a wire( use a wire and connect the ends this is so you can get all the nuts out after you are done), at least 18 inches worth and have you and a buddy shake the s hit out of it with some solvent in it, this will remove a lot of the rust or have it steam cleaned, usually a rad shop has the capability for this. If you do do the shake, still filter it at the tank.

Best of luck!