For cyl head chambers - piece of flat plastic with a small hole in it near one edge over a chamber, sealed against the head surface with a smear of oil or grease. valves should seal themselves if in good condition. spark plug in obviously. The hole is to pump in fluid with a large syringe with ml scale. The hole will need to be slightly larger than the syringe to allow air to escape as fluid enters. Having the hole near an edge allows you to tilt the head slightly to keep the hole higher to allow air to bleed out as you fill it - if it were in the middle you'd have trouble getting air bubbles out.

Pistons - same sort of process to get the capacity of a dished piston. For a domed piston, nick a container out of the kitchen with ml marked on the side. Fill it to say 100ml then dip the piston in just to the edge of the ringland, so just the dome is in the water. The scale will show you how much water was displaced above the 100ml starting point and that's obviously the volume of the piston dome, as long as there's no air pockets in valve recesses. If there is, you can fill them with playdough or something before dipping them, and then measure the valve recess by filling it with fluid. It's fiddly, but that's life.

Exhaust VSS are considered optional by some as there isn't any real vacuum in the exhaust to suck oil in, unlike the inlet side. But high speed air leaves areas of low pressure and can suck oil in, plus crankcases and valve covers get pressurised slightly. So for the sake of a few dollars and a minute's work I always use them on exhaust valves as well. There's zero benefit to leaving them out.