In the end I just made one out of 1" square tube.
Various lengths, holes drilled as needed, welded together and bolted on the tappet studs.
Looks a bit agricultural, no offence to farmers.
The head with water in 1B was the first effort.
The back of the head, and the outside edge came up 2 or 3mm quite easily.
The front inside edge, at the 1B end, was stubborn.
It looked like it was stuck on only 2 or 3 studs at most.
Nothing to loose, I put a 2 ton bottle jack between crankshaft and head,
There was a 6mm thick alloy plate on the jack against the underside of the head for protection and spreading the load.
The crankshaft end had a bit of alloy to protect the surface.
The jack is old and the seals leak a bit, but I reckon it was pushing up with at least 1 ton.
That did not move the 1B inner edge at all.
One of my employees with a much beefier build than mine brought in his FBH.
I pumped the jack while he swung the FBH and after about 20 hits the head budged.
It is now up 5mm all around.
It is amazing so much force and impact was needed, and it might only be 2 studs causing the trouble.
Once the head is off I can see what gives.