Classic Cycle City on German eBay is probably the best alternative.
My K6 got them when I restored it to season 2014.
I checked the slack May 2023, 65.4mm after 44.000 km!!
I measured at least 5 times.
I think slack was just under 65mm when installed in engine not yet started. I had checked slack 15.000 km before last time, 65.4mm.
So no further slack despite minimum 104.5whp and 4-5 dyno runs with 4 WOT runs each time.
The rest cruising around no racing. Bike is a street bike.
Engine history after back on the streets 2014:
836 around 80-83whp depending on cam used.
2017 1005cc around 90whp.
101 whp 2020, 104.5whp 2021, 107.5 whp 2022.
It ran better 2023 but no dyno. Mostly midrange due to correct needles.
My CB750 K2 (mostly stock) got BMW car cam chains.
See this thread that discuss stronger primary chains.
I commented with my CCC chains and BMW chains with photos.
http://forums.sohc4.net/index.php/topic,154183.msg1780341.html#msg1780341The strongest there probably as the CCC chains that have correct lenght from the very beginning.
Cut 70-71 links car cam chains and rivet them correctly as 68 links need new master links with correct tool to make my mind free of worries.
The BMW car cam chains 68 links from the beginning look as CycleX chains.
I have a new set of CCC chains waiting to be installed in an engine build. I guess around 90-95whp if I stay with 890cc.
Case is milled to welcome JMR Billet block 1005cc.
I might be curious if the pistons gas porting will change something.
Those chains will survive lots of abuse, that's for sure.
I can take photos of my new set of CCC chains compared with BMW car cam chains and old CB750 stock chains.