I put the A12 in both our buggies and they work great. A lot more lift and duration over stock just by looking at the cams side by side. I put new ncy11k rpm springs just to be safe because both motors have about 4 riding seasons on them. The top end didn't gain much but better low end and mid range. My red 155cc buggy has better top end than the 183cc due to the heavier piston and longer stroke.
As for big bores the next motor I do will be a 60mm and a 3mm crank kit. The 62mm piston is cool but the boring was not worth the gain and it has more vibration due to the larger piston and runs hot. I bought the ncy boring tool for $120.00 plus $25.00 shipping.
Not the most accurate bore but it worked. If you go with the 60mm piston you can grind the case by hand but it will be shade tree.
The main thing is to get a piston kit with a side wall at least 1.25mm thick as far as I am concerned. The srp 155 kit in my buggy has a thin .90mm side wall and the 62mm srp kit in my wifes buggy has a 1.35mm. The stock cylinder is almost 2mm thick on my last engine.
This is all my own opinion with the results I have come up with over the years. But I will say you get what you pay for and I got a bad 62mm srp kit with a crooked piston pin bore and was able to get another piston to fix it.
Stick with the Taiwan parts for sure.
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