My neighbor across the road has a 69 F100 with a 390 and it's gas tank is behind the Seat in the cab.

Was his dad's truck, who had bought it brand new back in 1969.

I helped him chase a fuel starvation problem as well.
Like many he had replaced a ton of parts some more than once.
As it turns out the hose from the tank to the steel line was collapsing.
This was around COVID time so that line was 50ish years old.
Replaced that and problem solved.

It drives me crazy seeing especially on the "restore a rust bucket in a 1/2 hour" type tv shows where they run a rubber fuel line all the way from tank to fuel pump the length of whatever car they're working on.