MOPED ARMY

I’d personally opt for the same make for all 4, that way you know the stroke / bore will be the same. Look for something with a cheap Chinese market so you can afford to experiment. Like below...

https://www.ebay.com/itm/Gas-Chainsaw-Engine-Motor-38mm-Cylinder-Piston-Ring-Part-for-Stihl-018-MS180/223694081535?hash=item341534cdff:g:hcoAAOSwovNdmGKt

I’d aim for what was common from Home Depot or Lowe’s, like Echo or Roybi. I gave away my last gas one a couple years back or else I would send you some. Post pics of your project if you can, sounds cool