I needed the upgraded pushrod fr my 500 K0 (part of the upgrade kit to improve shifting/gearbox problems)
I found two on eBay in two pieces that the seller claimed were the proper 'two-piece' part .. which doesn't exist.
So then I found a CB500T one, which turns out is the CB500 323 500/4 part. ...but doesn't suffer breakage in that model and usually sold a lot cheaper (as most 500T parts are).
Also beware of the CB500K3 gearbox (will be import , not sold here) if you want to replace an early K0 -> gearbox ... the K3 gearbox is from the later 550 model.
OK Trigg. I know this is all old hat to you but may be of use to others on here.