the two panels on top of your tank statement throws a wrench into things. In the passenger side rear about a foot in front of the rear body panel of the trunk there is a plate that is held in by 5 or 6 screws, that is the cover (paneL) that goes over the fuel guage sending unit. Where is the other panel located (1) and is your tank still in the car? (2) was this car sitting for a while before you scored it? (3) Is there a evaporator tank in the passenger side of ther trunk area...it could be seen by pulling back the plastic trim in the trunk area (if you are lucky enough to have that on your car)4 and can you post a pic of the fuel vapor thing on the firewall that has been bypassed? I have tried to look that part up and can't find it.
I ask all of that to try and put a little more info out there and to see if you have a crank or evapo type system and that may make some ideas pop out in someones head.

As to the question about did the car sit for a while before you got it...maybe the gas tank needs to be cleaned out, had mine done by a radiator shop.

OK, I'm done rambling for now and asking silly questions that may or may not get us anywhere ....but we can hope.