You can completely remove the valve guides, BUT, that is not the best practice. Bullnose and reshape the intake guide. Lay the back side of the intake guide back on the biased side of the bowl. Spend alot of time reeading up on how to reshape the valve seats, just don't go hogging on them. The valve seat shape has ALOT more to do with good head porting than meets the eye. Dont spend alot of time on the port floors, other than widening them and smoothing out the short side radius. You can (typically) remove about .10" on the port floor. spend most of your time moving the roof up and widening the valve bowl as much as you can. Don;t completely remove the little bump on the short side, as ther is water real close there on some heads. Just increase the radius, to smooth it out some.
Read ALOT before you even turn your die grinder on. Speedtalk.com has a bunch of real knowledgeable guys on there that have posted alot of good info about head porting. READ, READ, READ. Then read somemore. Look at heads that have been ported by a pro.
Good luck. After your first set, you will understand why they cost over $1K ready to bolt on. LOTS of time is spent. Wear good eye protection, good respirator, hearing protection, and take micro breaks and give your hands and forearms a rest. It's HARD work. Rewarding, though.