I just went through all that. I have a 1960 super 88. Fusick had the best price for sending units. The problem I had was the "sock" filter...
I bought mine through a chevy supplier.
http://www.lategreatchevy.com/produc...dept%5Fid=1272
The sending unit is on top of your gas tank. I wasn't getting a reading on my fuel gauge so, I got the sending unit. (USA Auto Parts0 for $129.00) Fusick had the same unit for $69.00!
I dropped the tank (9 gallons of gas, premium still in it) took it to a shop to have it blasted, some shops still can do the "renue" process, they did something callled rattling, a process of shaking beads around to dislodge the chuncks of varnish, etc. Then, the spray an inhibitor.
At Late Great Chevy, be sure to check your size. 5/16 or 3/8
good luck.