The Manual states 13" between centres, but I've seen 12.9" mentioned also (no biggie!)
Ikons perform very well, and are well worth the investment.
I've got a pair of Falcon shocks ready to put on my proddy racer, but as I haven't built the bike yet I can't comment!
They build to order and aren't as expensive as you'd expect - depending on what your requirements are, of course.
They're still not cheap, though. It depends on what level of performance you require - Hagons are OK for a 'daily rider', and still make the correct type for the Commando.
1964 650SS CR project
1971 Production Racer project in progress
1975 Ducati 900ss x2
1976 Triumph Bonneville