More interesting info I learned - S2K pistons can't/shouldn't be used in K-series blocks since it has iron lined sleeves. The S2K pistons were designed for an aluminum-matrix cylinder. I'm not a metallurgist, but this is the information conveyed to me by a respected and reputable source.
Well if you bore it out to 2.2L, you should see a torque increase, if you want to rev higher, you're going to need new cams, and probably some new valves and valve springs, Not too sure the stock vavles can take 9k+ dailly without bending or breaking.
About the pistons, you're better off getting forged over S2K stock.
You will need tuning if you haven't thought about that yet, the K-pro and several hours on the dyno should do the trick.
Cost, I'm not sure but to straighten this out a bit:
3.3858in = 86mm (stock bore)
It looks like he wants a .050" over bore so thats
3.4358in = 87.2693mm
Maybe you should just ask for a 2mm overbore, which = 0.0787 in.
Your final bore would then be 3.4646in or 88mm
Please just use metric, its so much easier.
If you want to get 2.2L of displacement your best bet might be to increase stroke, you could go with 88mm bore x 90.7mm stroke = 2206cc / 2.2L
In comparison, your redline would go down, but stronger internals will help that.
86.0mm stroke @ 8,800 = 4,965 ft/min. Stock K20A
90.7mm stroke @ 8,342 = 4,965 ft/min. Stroked K20A
When you stroke a K20 your r/s Ratio will be decreased because you will need shorter connecting rods. If you use a K24 you will see two differences, it has a stock bore of 87mm (+1mm vs. K20) and has a taller deck height which gives room for longer rods to go along with the stroke. The K20 stroker and the K24 hybrid will both be good setups.