125cc cylinder replacement kits...

[Ottomic]

I've got a couple projects (three pit bikes and one cart) with 125cc engines and I'm looking to just replace the cylinder and piston altogether.

One in the cart is a bit rubbed off, but reads "152FMI" and I'm guessing that the 52.4mm kit from amazon should be just fine, yeah?

The pit bikes are

154FMI
FH157FMI (two have this mark and are identical looking with "qiye" marked casings)

I've read a bit here that the two digits in the middle (52, 54, 57) should be the bore diameter, but I'm not seeing any 57mm bore kits. Am I just zoning out and completely missing them?

I'm guessing the stroke length would be different between these engines in order to give the same "125cc" displacement between the different sized bores, so the wrong kit could lead to headache or a piston crashing into the head.

I've had great success doing such swaps on 110's, 70's, and 50's, but wanted to tackle these bigger bikes.

Any help, advice, links in the right direction/previously discussed threads would be much appreciated!