John, welcome to the Stovebolt Page Bulletin Board!
I can make a suggestion on only a few of the questions about your truck. More knowlegable folks will soon chime in with more help.
Don't change out your gas tank sending unit just yet. The problem with it make be something as simple as a poor ground, especially since the truck's been sitting for that long.
I don't know what that fitting that goes into the head for the temp sending unit is called, but I think they're still available. Send off for a catalog from this site's sponser, American Classic Trucks.
Check the Frequently Asked Questions area on this site and you'll get some answers pretty quick.
Also, you can do a search, using key words from your questions....you'll find a lot there too.
See if you can post a picture of your truck, the folks here, (me especially) love pictures of old trucks.
Sounds like you've got a good one, especailly since it was your grandpa's truck. Ask more questions and let us know how it's going.
