How about this online version? SDP/SI
Yeah found that but you cant quickly and easily compare different pulley combos and belt lengths.

I tend to make motor mounts with about 20mm of center distance adjustment, as that's generally enough to allow changing the ratio whilst only changing one pulley. That might cost you less than buying (or making) 4 or more pulleys per axis.
good point but I was thinking along the lines of a quick change system with the pulleys all fixed permanently and just move the belt over like on lathes or mill spindles. anyway going a bit off topic.