I sure wish I could help you more. I was trying to find out about which tank is right for my KX 250 and found little information. I did find out that in certain situations both tanks fit , or don't fit well on certain models. IE Clarke's fit well on XR 400's but not the IMS, on XR 600's the IMS fit well, but not the Clarke. I feel both companies make good tanks however.I did get an IMS tank used from Smitty (DRN member, Thanks!). the area where the petcock mounts is curved and leaked horribly. I carefully applied black silicone and have not had a problem since. I used the search engine Google.com and typed in "Clarke KX 250 and IMS KX 250". I got results that sent me to message boards of riding clubs around the country and thier want adds. You might try looking up a local desert or enduro club and go to one of thier events and see what they are using. Good luck and post us what works out.
:D :D :D