Aye Andy,
Personally wouldn't bother with the 'bull', just clean carbon off with a lollipop stick and cocktail sticks. If there is more effort required than these will take to remove the carbon, are you revving it hard enough? ;-)
Opinion varies between polished mirror finish and clean unpolished surface. First assumes greater flow hence total volume of charge to burn. Second assumes 'golf ball' effect which provides lots of minor eddies in the charge giving better atomisation and mixing of the charge, hence a more complete burn of the charge. The shape of the ports has more effect than either finish on potential charge volume.
You also mention that a lot of alloy has been removed from around the valve guides. Whilst Slipstream know their stuff, I just wonder if too much has been removed, reducing support for the guides and allowing them to flex at high rpm. Common problem with over enthusiastic removal of alloy on Duke single heads in the inlet port, when trying to get them to breath properly. I don't think I need to elaborate on the consequences of flexing, loosening, valve guides at high rpm!!! :-O
Finally, after grinding in your valves, finish off with Brasso or Solvol to get really smooth seats. Wash away ALL traces of grinding/polishing compound. Smear seats with a touch of light machine oil before assembly and some graphite and engine oil on the stems to ensure they don't 'pick up' when first starting.
All the best, Bill