I appreciate the feedback, but I got it started. Issues were in the wiring and solenoid. The starter itself turns it over just fine. Not sure if you saw the post back there, but I'm running an Keihin FCR38. Took some slight frame modifications, but works very well. FCR's pop up on Ebay pretty cheap all the time in the US.
Yeah I saw that - I've had to do similar mods to get the dellorto in. I still have a bit more tidying up to do on it. The Keihin is taller than the dellorto so I don't think it would work well on my 250 as the frame is lower than the 500 (on the 250 I can't use the upper engine steady because there isn't space for it!)