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I would use the Chain Length Calculator @ www.rbracing-rsr.com/chainlength.html

If i would convert to a 530 chain (630/15/35) this would be my setup.

 

But now we went from a 63” chain to 65”.......

So what I gathered so far is you can put a 16/39T set up or 17 tooth front with a 40T or 42T rear sprocket, but then 16/39 gives a .410 ratio and 17/40 gives a .425. An d just to mix things up a little more, a 16/40 ratio would give .400.

17/42 would be closer to original set up, we just need the number of links now....

JL

17/42 would be closer to original set up, we just need the number of links now....

JL

Put in the Center to Center of both sprockets and the calculator give you the numbers of the links....

Sprocket diameter

13T 630 = 3.13"
16T 530 = 3.20"
17T 530 = 3.40"

In other words, the 16T 530 front is the closest match that's not smaller (which you shouldn't do.)  

Got to my dealer this week to order chain & sprockets for my 1984 KZ750L.
I compared prices for 13/35 & o-ring chain in 630 and 16/42 & o-ring chain in 530.
Well, the price of the 630 chain alone was a few bucks higher than the price on 530 chain AND both sprockets.
So, I did not hesitate and ordered 530 parts.

Maybe online it would have been possible to find a cheaper 630 chain but I prefered to focus on something else and decided right away for 530 components.