Hi Bob,
I've provided some thoughts after each question.
1. Do you think the cells can be air pressure tested for leaks or bad seals while still in the car (i.e.; seal the back and front nipples, add an air intake valve and pressure value, inflate to 10psi ( ? ) and watch for a pressure drop, hissing sounds, etc.)?
Sure, you can buy a rubber plug at the hardware store and put a Schrader valve in it and plug both nipples and with a bicycle pump do a 10psi leak-down test with a tire gauge.
2. If the cells do have to come out, when and how do the fuel sender wires get detached? Besides a broom handle, any other little tricks?
Under the carpet on your doorsill you will see a round inspection plate. It is access to the fuel level-sending unit. You will see the wires and can disconnect them from there. After they are disconnected, pull them and tape them to the sill. You don’t want the cell to snag them on the way in our out.
3. An finally, can you give me the exact inside, outside, and height dimensions of the front fuel cell filler neck nipple? I would like to order the a set of check valves before I start taking the front of the car apart.
Unfortunately, mine’s back in the car. You can see yours by pulling the access panes behind the front wheels. The rubber neck at the base of the steel filler tube is actually the neck of the cell.
In answer to an earlier question, I made replacement gaskets for my cell with NAPA gasket stock coated liberally with Permatex HYLOMAR. It won’t leak but you can pull it apart later if you need to.
Bob, I think you still may have my phone number. I’m off tomorrow if you want to talk about it.