Saving Old Seagulls

Running mongrelized CPCL with short haft, Amal 416 carb, etc. On a barrel test after number of minutes at moderate throttle, I noted cooling water coming out of block was getting hot. Eventually got hotter than I could comfortably hold my hand in. When I shut down motor, the exhaust tube and block were sizzling hot. Recently when running on my boat the motor slowed down and stopped, but started easily when on trailer minutes later. Leads me to think the block may be cracked a bit and when engine warms up crack opens and lets water into cylinder? Maybe? I have another block of unknown provenance and could perform major surgery and swap blocks further mongrelizing the motor. Otherwise, motor starts easily and sounds good. Observations?

Try taking the head off and have a look. Just because water is flowing out the telltale hole does not mean that the block is not clogged up with rust.
The engine will slow down and stop if you heat seize it and once it has cooled down a bit, it will most likely start again.

Nudge:

Many thanks for response.

Just pulled head. No signs of crack. Might it be head gasket? When I put head back on, what should I torque bolts? Should I use gasket cement?

When I put head back on, what should I torque bolts?

Try this thread:
viewtopic.php?f=2&t=6040

Should I use gasket cement?

Just use a smear of high temp silicone
https://www.google.co.nz/url?sa=i&rct=j ... 2789162370

Nudge

Removed head. Used permagasket, refit head, torqued to specs. Started first pull. Ran in barrel for 15 minutes with gears engaged, no recurrence of problem. But a bit worried that original problem might have also involved coil.