KF-3 & KF-3-1 have their own tank part # Later KF-3. KF-5 and Mark 5 share a tank with a different part #. The later fits all tank will be easy to find. The early KF-3 tank will be harder due to low production. Using later tank with early KF-3 is doable, but, that may require some more parts as well, KF-3 had many changes ,