Thanks Ed,
Your right about the lower counter bore surface area, very limited on the older blocks. The copper rings are all superseded to steel now so I’ve ordered 6 steel ones. The pistons are different to, they measure the same so compression should be the same but one lot have 3 rings and the others have 4. I’m just about over it now I don’t think it will matter as long as the compression is the same. If it plays on my mind to much I might give you a call.
Thanks again
Mark