I would attach the nipple to an old plug as long as you smash out the porcelain .
Block the intake and exhaust port ,rubber hose and wood plugs / plastic etc and hose clamps would work. for the intake.
The exhaust you may need to g clamp a flat plate over the exhaust port with a gasket or flat rubber inbetween the plate and the port.
The piston is at bottom dead centre for testing and you can rotate after you have vacuum applied.
I don't think the bore etc will be scored at 79 psi. but is easy to check.
To see where the leak is if you have one ,you would need to use soapy water where you are checking for a leak so if head gasket and the 2 port block offs aren't leaking then you know it must be crank seal with a pressure test.
With the vacuum test you will know there is a leak if the needle falls.
