Fuel Tank Options - '78 Audi Fox

[urq]

The fuel tank on the old '78 Fox is getting pretty rusted up inside.  The
car has one of the "drop in" style tanks ... not best known for safety ...
I'm wondering if anyone is familiar enough with the fuel tanks on the newer
models like the 4000 to know if there would be much chance of fitting one
between the suspension towers on a Fox.  Now that I'm thinking about it, I
bet the biggest issue woiuld be fitting the fuel filler neck ... oh well!  I
suppose if anyone in the area near San Jose, CA has a possible donor drop in
tank in good shape I'd consider that as well.

TIA!
Steve Buchholz
San Jose, CA (USA)