I bought a Speakeasy T-122 tube preamp off Ebay for $300 (saved me about $150) and in the little reference sheet it lists all the models compatible with which preamp.
T-122
30A, 30C, 31A, 31H, 21H, 22H, 22R, 122, 122R, 122V, 122RV, 142, 222, 222RV, 242, and 122A
T-147
31W, 44W, 46W, 25, 45, 47, 47R, 125, 225, 145, 147, 147V, 147RV, 245, 247, 247RV, and 147A
9 Pin
760, 770, 825, 900, 910, and 925
11 Pin
122XB, 130, 315, 330, 412, 615, 715, 716, 722, 723, 740, 750, 771, 815, 820, 822, 840, 860, 912, and 914
So if you're interested in connecting your modern keyboard to a leslie, this is the way to do it. Just look and see which preamp you leslie falls under. I'm currently waiting on the arrival of my Leslie 44W (found it on ebay and bought it for $500). I plan to convert it to a 142 cabinet (122 amp).