I had a couple long beds with the smaller single tank. That being said... When I replaced em I got the larger tanks.
If the truck is a long bed and came to you with mismatched tanks it's conceivable the PO had one, of a pair of 16-gallon tanks, rust out and replaced it with a 20-gallon tank. There's no reason not to... Or they were a cheap ass and replaced a rotted out 20 with a 16...
IIRC the fuel tank frame supports will fit either tank... I don't recall buying new ones to replace serviceable old ones... The senders definitely fit either tank.
As far as the 305 goes. It's a lower power engine with no performance modification potential. If it runs well and doesn't smoke... it's free and it's much better than no engine.
When I got the short bed I was told one tank has rust holes, but upon looking under the truck they're both pretty rusted and I can't tell which one is supposed to have the hole.
I also have no idea about the tank switching valve: which tank it's pulling from, if it works, is the switch works, or how to test the valves or the sending units.
Any idea of the oil gauge is electric or mechanical?
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