IIRC they should be the same. I have sold a few off junk trucks for members that had mid 80s trucks in general.

I think the straps are about the same and the tanks are different size/gallon.

my 35 gallon tank in the 85 stepside went from axle to up under the seat area.

stuck a 18 gallon tank right in there with those same straps. went from axle to front of bed area and not under the cab.

I had a hole drilled in the bed on one of those trucks to get the nut on the stud end of the strap.

I have made a couple easy enough. but now the 440 truck has a fuel cell and I used a 70 mustang tank behind the axle (like a RC/TD) in the 85 stepside.

I would have 2 set but just junked both trucks last month. sorry.