HD mag chain is
Magneto chain (1/2″ x 3/16″)
1 off IWIS type P83Y x 68 links
1 off spare connecting link to suit type P83Y chain
This was recommended to me by Andy Forsdick who had advised and supplied chains for racing use over the years
I have not used this chain myself, but apart from those I suggested use it, the only comment was that it is a bit “Chunky”, but then if you need something stronger, then this is understandable.
I do not use it only because my racer drives like a Sprint Special. I.E. it drives the mag from the clutch drum and way back in the 1970’s, I converted it to a belt drive and never have to touch it. Eddie does these conversions if anyone is interested