I did a lot of searching and all I found conclusively is that the big 40-42 gallon sub tank won't fit in a K5. What I want to do is put a 31-gallon tank from an 89 3x4-ton Suburban in my K5. Will this fit under the stock skidplate? Is it the same as an '89 K5 31-gallon tank? I will pick it up today if it will work. Thanks.