[Saint aka ML]

The starting motor comment is valid for early carbed m900 when they went IE they also changed gearing on starter motor.
However nice clean earth is good idea either way.

There is no real side effects to off the shelf HC pistons.
Whom ever fits them should adjust timing (retard it), adjust fuelling a bit and off you go. If you can fit adjustable belt pulleys and get them to dial in cams. All is cheap and slippery slop to modding hehe.

It will run bit hotter so at 30c stuck in traffic you will feel it. Nothing to worry about.
You will have more low and mid torque, if you do fuelling on dyno you could get 2-3 bhp.
Main benefit is torque and with correct timing throttle response.