The area an inch above and an inch below the valve is the area you will extract the most gain, in porting of a head. Say 70% as opposed to 30% elsewhere in the port. In saying this concentrate in that area around the valve for the most benifit.
Of that area the most gain will be in the tight radius below the valve.
Think where air has to bend around a corner, the tighter that corner the more air speed lost.
That sharp corner below the valve has to be radilized as much as possible without compromising the thickness of the head too much. A large radius bend is much beter than a small radius bend in this area.
Flow will be gained by grinding the valves and seats with 3 angles with the middle centerlized and as thin as possible.
Where the valve guide enters the port needs to be reduced in radius and knife edged where possible. A general clean up of the ports is all that is needed as enlarging ports will require the use of big duration cams and bigger carbs with power shifted higher in the rev range as a result.
The same can be said about larger valves, original sizes would be better or only slightly larger, as the biggest you can fit will lose air speed low in the rev range.
I have been involved in building drag car and street car engines for a number of years and this is a generally what i have learnt ove time.
To sum it up Big power and torque gains comes with big ports, valve, cams and carbs high up in the rev range.
While moderate gains in power and torque come lower in the rev range with smaller ports, valves, cams and carbs = higer air speed.

Hope this dosen't sound too hard, and helps.
Give us a yell if you have Q's.