I think the later years have a smaller opening where the filler neck goes into
the tank.  At least, that's what I found when I replaced my '80's tank with a
dealer part.(Nearly $400, wholesale)  Being impatient, I used a drill to take
out most of the difference-the '80 inlet was about 13mm bigger in diameter
than the tank I got- and then finished off with a die grinder for a snug fit.
I filed the edges off so as not to cut through the gasket and have been ok
since.  I did rinse the tank with gasoline and blew it out with compressed air
several times and well as a quick filter change after two tanks.  The only
small drips I get now are when the tank is full and the van is leaning steeply
to the driver's side (which is rare, but up in the mountains of VA, it
happens) due to the overflow vent tanks either being cracked or having poor
gaskets, not my handy work.  So rare, it's livewithable, for me. Huge
disclaimer about safety here, I did this in a fully equipped shop and took a
full, patient afternoon to make sure everthing worked out ok.  Be safe and
don't smoke while working on gas tanks!  Patrick