The first thing I will say is stay out of the valve seats.
To many people have given me heads that require a few new valve seats because someone has gotten to wild with the die grinder.
For cast iron you will need to invest in some carbide cutters.
They are a little expensive but should last you forever.
Then you will need a porting kit.
I would try Goodson for your porting supplies.
I would first remove all the parting lines and knock off any casting flash if there is any present.
Think radius/smooth.
No sharp turns of rough edges.
In a street car I would try and keep the finish in the 120/180 on the intake side to try and keep all the air/gas atomized.
The exhaust should be made very smooth.