Thanks, that might be an option.
I think you have to adjust the XJ6 cilinderhead a bit to make it work? Does the XJ6 SIII not have bigger exhaust valves? Maybe blocking some coolant holes?
Another option i have is using the Big Valve Military head?.
I know somebody that still have these new in the crate. But I don’t like the fact that it’s not an E-type head.