I've been following the saga of CB750 primary chains for over 10 years now. Back then I bought a pair of (astronomically priced) chains from M2 (?) in the US. I'm convinced modern chains are hugely superior to those in 1969. I had a CB750 in 1970 and had to change the huge and heavy (530?) drive chain every 3 - 4000 miles. It's amazing to think that a 300 BHP Moto GP uses a 420 chain. I believe the chains I bought from M2/USA are Regina chains so I'm confident they can handle the 90 BHP my race engine will make. I listen closely to what Brent (V&H) says about chains and have fitted his cam chain guides in my 1100F race bike engine. Its very interesting to follow this thread because, I've been collecting the parts for my CB750 SOHC race engine for 10 years and now I'm finally putting it together.
I bought the Cycle X primary chain tensioner some years ago - but now see the recommend the standard tensioner?? Bit worrying ...