The 600 was a specialty multi channel model and has a really bizarre tremolo switching scheme. So, if you sell the Conn separately then remove the hookup kit / board as the Leslie is pretty much useless without it. I think the rotary channel had a treble horn but a rotosonic drum so the Hammond crowd might not care for it. Also bass was carried by a separate stationary channel IIRC. As far as value, beats me. Probably not much. There has been a 600 on eBay for months, now at 450 OBO, no bites. If I were you I would try to sell the Conn and Leslie together since it was designed to work with organs like the Conn. Do you have both tremolo controls - space generator and rotary?