I bought an ignition and key off of EBay for 12 bucks which fit "some old Yamaha", and tried to apply it to the XJ750R. Didn't fit. So I removed the guts of both and ended up using the top end of the newer one with the bottom end of the Seca and it now fits and works well. The internals were very similar but the bottoms were different, especially with the handlebar lock.

Just thought I would pass this around since new ignitions are stupid expensive and keys seem to fetch 9.00 on EBay lately.