Here's more info from amprepairparts.com
There are 3 different replacement reverb tanks listed for Kustom amps.
4FB2A1A replacement for K200-A (that's the one in my amp)
4FB2C1A replacement for K100-2,K100-5,K150-2,K200B5,K250-2,K250-4,K400-B5
4FB3D1A replacement for most Kustom amps from the 60's & 70's.