Think the K1 that Pete has, the seller (sandcast guru) used the later gasket and fitted O rings for extra sealing. Honda issued a bulletin on it and sold special square section 'o'rings as mentioned in the bulletin. I bought some Viton ones as used on Pete's K1. If I have not given you some already, I can dig you out a set.
Its SB #42 Cylinder Head Gasket Oil Sealing but it was removed from the SOHC4.net site
Original SB 'O' rings 12115-300-305
http://www.ebay.co.uk/itm/NOS-Honda-OEM-O-Ring-CB750-12115-300-305-/191011621578see
http://forums.sohc4.net/index.php?topic=63310.0Maybe a quad ring seal would be more like the original Honda ones. I will investigate Rich
This is from the guy who sold Pete his K1
"Yes, you can use the later "large hole" gasket on the early engines, but be aware that you are actually creating a small cavity that oil can sit in at the head / barrel joint around the 8 drain studs. On the odd occasion that I have used these later gaskets on early engines, I have fitted 8 "o" rings of an appropriate size from an engineering supplier to effect a seal.
Any later K series barrels will go onto a '69 motor, but as you say, you just have that "spare 6mm threaded hole (which can't really be seen anyway once built up sandcast). It is only obvious that later barrels are fitted if they are the late K1 and onwards die cast type which have a different fin profile at the ends."
