This is a really strange chain to me. A 530 chain such as used by my Honda 500/4 and lots of other motorcycles up to more that 1000 ccs, is only 3/8" wide, although 5/8 pitch.
I think the numbers (520, 420, etc.) are Reynolds numbers, developed by the Reynolds company who seem to have been a standard in chains and are usually used to designate chains used on motorcycles and other high speed applications.
Small motorcycle chains, and bicycle chains, are all 1/2" pitch with widths up to 5/16" (428).
The measurements you have make no sense to me, especially the pitch, as it does not even translate successfully to a metric measurement. Are you sure you are measuring from center to center of the rivets?
In any event, this chain appears to be wider than any "standard" 1/2" pitch motorcycle chain.
There is a different range of chains available for machinery, farm, industrial, snow blowers etc., possibly it is for one of these applications.
Are there any markings on the side plates of the links?