I’ve had 8 heads crack tested (4 x closed chamber & 4 x open chamber) and they’ve all come back cracked, either through the combustion chamber or around the two end bolt holes closest to the exhaust manifolds. I’ve just payed for a NOS set of closed chamber heads, which is what I was wanting anyway to chase the CR of the Commando. I know I’m going to have to alter the bolt angles on my LD4B but I’m ok with that, as you said these Edelbrock manifolds are getting hard to come by and these cracked heads have put a real dint in my budget. I appreciate you taking the time to reply to me, it’s really appreciated mate.