bsdectr
The size of gas tank is being debated. One mechanic claims it is 22 gal. Another says it is 12 gal. It measures 33" wide X 23" long X 7 1/4 deep.
I was told it is 12 gallon, and 12 gallons seem to fill it.

J. C Whitney's 22 gallon behind rear acle tank is OK for measurement, but does not have o-ring, and they don't know where to get one!

Check out lmctruck.com I don't know about the vans but the 89 and my 95 have 19 gallon tanks front and rear. By saying breather tubs are you talking about the filler necks that have the extra tube in them that lets the air escape when you filling the tank. If the trucks are the same I have two.