Gas Tank Replacement

I"ve got two questions about replacing the gas tank on my 1979 Chevrolet Caprice.

The 20.4 US gallon tank needs to be replaced on my 1979, and I want to replace it with a 24.9 gallon tank used on the 1980 and later models. I've checked and the sending units are the same for 1979 and 1980, but are there any other complications I should anticipate?

Also just out of curiosity, I tried fishing two different diameters of hose into the tank to drain it, but both jammed at the base of the neck despite all my best efforts, so ended up draining from the front by pulling off the fuel line to the pump. Is there a trap or something at the base of the neck to prevent siphoning? Just curious.

Thanks

My preference would be to get one for the 91-96 cars. Plastic won't rust and weighs less than the steel tanks.

And, it's a swap that's been done (proven) on at least one 1989 brick-model Caprice. So it should work fine on the 1979.