I’ve never messed with a rear handle 193, but several 193t-c which should be identical in all but the handles.
You’re looking at a stratified intake. The upper two ports only move air. They open into the piston windows and then puff air into the transfers so that the exhaust is chased out of the cylinder with air instead of raw fuel. Just ignore them. It’s technology designed to meet emissions requirements. Unfortunately the third port is the fuel intake and it’s bounded by the piston windows, so you can only gain a tiny bit of width there.
The rest of the saw is a pretty classic design. The weird tunnel scoop above the exhaust is designed to make starting the saw easier and unfortunately reduces compression. This is also a clamshell design so it’s very difficult to change the squish.
I recommend you widen the exhaust, raise the transfer uppers 2 degrees, lighten the piston where possible, smooth everything real nice and slap it back together. There’s also a baffle in the muffler (the cage thing on the cylinder side) that should be hogged out, and of course make the outlet bigger.
In the end you’ll have a slightly better 193. The Engineers were very budget minded in this design. You won’t find huge gains.