I put one of those '72 blazer tank kits in my '63 c-20. It was a perfect bolt in. The sending unit was another story. I had two new sending untis, one for the new tank, and one for the old tank. Take the actual rheostat piece off the one for the old tank and put it on the new one. That's the piece in the middle that the float arm attaches to. It looks like a curved spring. This will give you the correct ohms for the guage. My swap went without a hitch.
