As far as I know, the 1vj/3aj are the only ones with the air box under the tank and the oil tank on rhs behind side panel. To put different tank/seat on would mean different airbox or separate filters, and shifting oil tank. I think early xt's had oiltank further back on frame on opposite side from exhaust. Front tank mounts on 1vj are bolts, other xt's are round rubbers.
Guess you will have to mix and match or just live with the 'hippo' look of the 1vj. Am considering cutting down 1vj tank on mine to let air in to top end of engine. Will cut out fuel pump as well, and I don't need the 5gallon fuel capacity. Hope this helps, Neil.