Its funny, I tried 3, count them 3 BRANDS of rods for that motor in the last 2 weeks, and ALL of the rods, which were all different brands were like 77 MM Wide at the big end!
So you can't even fit them in the cylinders! Nutz huH!
Those motors are so cheap, if I were you, I would coat the stock pistons with ceramic coating, give the pistons slightly more piston to wall clearance, at like .0019 and go with that at 10 PSI.
Jeff