yeah, as fugly as the SP370 or 400 tanks were (kinda..I didn't mind them too much and better than the '78 TS series IMO) the longish slim lines could work very well on a dirt tracker
was thinking of using one myself for a split second till I spotted the RL250 alloy tank on the shelf
I've a great big fat/fat someone or other brand plastic long long long range tank or I have a giveaway DR600 tank that may work but again more than likely look hideous
I know they're green but aircooled KDX kawasaki tanks went close to fitting a DR500 when little else would..assuming the frame on the 370/400 isn't so far removed it maybe a drastic last ditch type option