Plumbers putty rolled into a string would be good for them pistons. Vaseline or sumthin' on the opposing surface to keep it from sticking.
For the dome volume, set the piston down in the bore a known amount....like 1 inch. Calculate the empty volume. A graduated beaker feeding a light weight oil
into the bore/piston using plexi glass for a top....subtract the 2 & there is your dome volume. I betch'a you can finger out the C/R from there....
