Re: porting a stock 103 jug...
First thing i would to would be open up the exhaust a bunch, not in the window of the port, but where the exhaust connects.
Then after getting comfortable I'd open up the transfers by 1/2 cm on top and bottom.
Lastly, I'd split the case and open up the intake a bunch - my favorite mod.
of course this is all what i WOULD do, although i've never ported a stock cylinder, I've only done massive work on cases.