G'day Geoff. Sprockets it is. It was a 520 conversion, but it doesn't have to be. You'll be able to get them in 530. I'm a bit iffy about the difference 520 really makes. I am sure it makes a measurable difference, but I'm not sure it's enough to worry about really. If I was racing and trying to extract every last Erg from the bike...OK. It's noisier and I'm pretty certain it'll stretch faster too. So 520 for me..Meh.
As for the difference in pull going shorter on the front and taller on the rear, It starts to pull easier lower down and picks up the front wheel under power a lot more. I've actually had it pop the front and hold it at over 100mph over a very slight crest. Yes this is the FZ6 I'm talking about. It revs a little higher for highway work, but for twisty riding under 115mph it's a fantastic mod. Wakes the bike up. Hope this helps some.
Cheers
Mike