Can you put a bigger tank in a 94 4x4 toyo

 

Anything can be done.

If you're asking whether a larger tank would bolt right in without modifications, that's another story.

 

To answer it easy, yes. and with no modifcation. From the mounting flange up is the same size on all 4 sizes. 13, 16/17, and 19 gallons.
The size diffrance is made up below. The 13 and 16/17 gallon use one size skidplate, the 19 has its own.
As it is lower, the 19 gallon will loose you about 2-3 inches of ground clearance.

 

Thanks went back with new 17 gal