Bad ball or an air leak in the fuel line anywhere from the tank to the carb.
If its hot it can be a bad/old impeller, blockage somewhere, or corroded water passages.
Sometimes it is hard for folks to accept the truth from people who have worked on many of these motors since 1968.----Have all kinds of parts for those motors.----Boxes full of good parts.
My guess is that you have never seen a cylinder wall of a " new condition " motor.----Your motor needs to come apart.----Needs to be bored and oversize pistons fitted.---Returned to new factory fit and finish.-----I doubt you can find these parts today.----Find good used parts on E-bay perhaps.----Good used block and pistons needed and perhaps more parts.
on aomci site you said it was running... hot. scoring aside and suggestions to junk it if it ran...have you found out why it is not cooling. and btw what compression#s did you get .
looks like its burned up pretty bad , scrap it and go on the search for a later motor.
"" unless it has sentimental value" , if so spend $1000 + in parts to get it up and running again.
