Thank you again everyone.
The block isn't drilled for hydraulic lifters, so I'll have to use solid lifters, my option was to change to roller followers, but given the extra cost of changing, I think I'll probably stick with what I have.
I've been using Valvoline ZR1
oil and the rockers have been regularly checked and adjusted if necessary.
I've got a borascope, so I'll check to make sure the inlet ports line up and if they do, I'll just machine the top surface as suggested.
What do the specs of my cam suggest to you?
Paul