Thought I'd pass on some more invaluable info!!
When going for a 520 conversion, you need to make sure you have the correct sprockets. This mod saves a little weight over 525. it's only a few hundred grams, but it will reduce hp loss to the wheel.
You need to make sure to get a front sprocket that is 7.1mm wide (as the std 525) on the splines. Otherwise if you use a std 6mm 520 one you will wear the splines out on your gearbox output shaft, and that will make you cry!! The JT part number is JTF434-14T. Do not buy the 520 conversion one for an 87 bike (JTF1439-14) as again it is only 6mm thick and will flop around behind the circlip on the shaft.
I like JT HDS non o ring 520 chains, but you have to keep them waxed up to stop them wearing. I have had good success also with the JT chain with o rings, and using the supplied split link (which has never given any trouble)
SV650 520 rear sprockets fit on the rear.
Nick.

I agree!

I've done something similar. I thought that there wasn't enough engagement so went for a DRZ400 sprocket (JTF432SC), which is 10.2mm thick. Then I turned down the spacer behind to make it all fit properly. It has loads more engagement now and no slop on the shaft.

Same here,
I used a drz sprocket with a talon sv rear and machined the front to fit.