It does not really matter whether you are building a stock engine or using a big bore kit as the rebuild details are the same. I was using new Shasta design 83.5 pistons and have had the cylinders re bored to match.
Normally the piston rings are fitted to the pistons and ready to install with the correct gap which should be between 0.004" to 0.016"
A good way of checking if the gap is correct is to place the ring into the cylinder near the top and measure the gap with feeler blades to ensure it is correct. if the gap is too small then the ring end must be gently ground down. Porsche made a special tool to grind the rings. When fitting the rings to the pistons look for a dot or sometimes the word top on the ring. This should point to the head of the piston.
Pistons will be marked on their top surface with a small arrow. This should always point towards the flywheel.
They are held onto the rods with a wrist pin that is held in place by 2 snap rings. These have a sharp edge and a bevelled edge, the sharp edge faces outwards. The snap ring should be positioned as in the photo below and when properly in its seating can be rotated quite easily.
Clean the pistons carefully with WD 40 and wipe clean. Make sure the piston wrist pins slide in and out easily. lubricate with some oil. Take a piston and MAKE SURE THE ARROW ON THE HEAD IS POINTING TOWARDS THE FLYWHEEL.
For pistons 1 & 3 it is easiest to install the wrist pin from the front (flywheel end) to the rear of the engine. For cylinders 2 & 4 it is easiest to fit from the the pulley end. Sometimes you will need to heat the piston with a hot light bulb for a few minutes to allow some expansion for the wrist pin to go in easily. The wrist pin is fed through the bushing on the connecting rod.
You can fit one of the retaining snap rings before attaching the piston to the rods, and then drive the wrist pin in until it touches the retaining snap ring you have already fitted and then fit the second retaining snap ring which holds the wrist pin in place.
Repeat until you have all four pistons fitted.
Now you need to arrange the piston rings. Starting with the the oil control ring (the lowest one on the piston) turn it so the gap faces upwards towards the top of the engine.
Now arrange the top ring with its gap facing towards the intake valve, the second ring gap towards the exhaust valve and the third ring (if present) towards the bottom of the engine.
Give all the pistons a final clean with WD 40 and paper towel.
We will be coating them with stp/engine oil mix before fitting the cyclinder heads.
Clean the insides of the cylinders using WD 40 and paper towel until they are spotless.
Fit the shim to the cyclinder. Line up the cut-outs in the gasket with the cylinder cut-outs as shown in the picture below.