Pistons ordeal: more pistons problems; two issues in one question

Question

So, still having problems rebuilding this old engine (Skoda Estelle 120, 70's, RWD, rear mounted engine). First of all: getting new parts is out of the question since I have no access to those. So I need to get this done with whatever (s)crap I have :) As I'm getting more into the pistons sets I have (3), I find the following problems in all of them:

Set #1: 4 pistons are good, flat tops, no dents, no scratches, slides into the cylinders correctly but the pins I have are 5mm shorter. Second problem (which I solved) is that the oil ring groove is square, and the oil rings I have (2 parts, one the ring, one a coil ring inside) won't work because these needs the oil groove have a concave inner face, to accommodate the spring ring. I fixed that by concaving it with a dremel and a ball diamond bit. So real issue is: pin is shorter. I have being told to put an extra piece in both extremes, ideally hammered down, as to correct the length, i.e, insert there 2.5mm bushes by force

Set #2: 3 pistons are good, flat tops, one had a deformity in the bottom edge by dropping, all of them slides well, rings are not a problem. Investigating that dent I see it had a very subtle small crack. Since that crack would grow with heat a pressure, using the dremel and a round stone bit I grind the deformity/crack off without reaching the reinforcement lip that can be seen in the photo. I learned about working cracks out this way but in glass, I have no idea if this would effectively stop the piston to crack. So question(s) are: would this affect the piston integrity? Looking for some balance, should I also grind the other pistons like this, controlling their weight obviously? And yes, I know this should be left smooth so it won't cut the cyls

Set #3: 3 pistons are good, dome crowns, but 1 piston is cracked at the bottom through the opening under the pin. I only could see this after I sanded them with fine grit: the dirty marked the crack. I wouldn't use that one. So I guess this set is doomed. As these are dome, and the ones in set #2 are flat I guess I can't just replace the #2's grinded off with one from this set, or viceversa, i.e, mixing the pistons (flat and dome), correct?

Overall: what's the best option I have? Would set #2 work well with that grind on the piston(s) bottom?

Set #1

Set #2

Answer 1

My suggestion is to go with set #1 without any modification to the pins or adding anything to the pins. While the pins are a bit shorter than what comes stock, they should work fine. The difference of only 5mm (or 0.1969") is not a huge one. These should be handle this size of engine without giving you any problems. I think you have too many issues with the other pistons to use any of them without giving you more problems later down the road. If the #1 set is complete and the pistons are in good shape, this is definitely the route I'd go.