Fuel tank selector valve is your issue...very common with these trucks. You can also swap the rear tank out with a Bronco tank for added capacity.
Before you spend $$$ on manifolds or anything, look around for some headers, used or new. Uncorking the exhaust with better flowing headers and a dual exhaust will help bring out more power. That big motor needs to breathe. Swapping to an aftermarket carb like a Holley 750 and bumping up the timing will make it really come alive, and should actually help give you another mpg or so.
Expect single digit mpg's with that T-19 4-spd, you could always swap in a later model "ZF" 5-spd if you really need the overdrive. You'll need the donor vehicle trans crossmember, as well as the, clutch, flywheel, and throwout bearing from the ZF donor truck. Stock driveshafts will bolt right back up, so it's a pretty painless swap. It should also help pick up some more fuel mileage.
Someone above mentioned gauges...definetely get some aftermarket gauges, mechanical is fine, Oil Pressure and Water Temperature, even a pair of cheap gauges are far better than the factory gauges.
Post pics when you can, I love these old Fords.
