You will probably have to modify the 60-66 truck fuel sender or the 63-66 panel sender. The flange and it's bolt pattern are usually all the same, the ohms are the same, but you will have to shorten/modify the pick up tube and the float wire. Don't install into tank until tested with gauge. Don't know why the 63-66 panel sender is different than 60-62 panel sender.
https://www.classicparts.com/1963-66...tinfo/23-528B/
https://www.classicparts.com/1960-66...ctinfo/23-527/
There is a universal sender also:
https://www.classicparts.com/1931-66...tinfo/23-522A/...NO FUEL PICK UP TUBE!!! It could be added however.
Do you have the old sender?