I'm a believer that a highly effective learning technique is to do something completely wrong the first (sometimes second, and third) time.
This is my first time porting a head enough to require removing the valve guides. I'm using a driver from Beam equipment.
Of course, the driver mushrooms the end of the guide so it grabs the valve. How should I fix it? I tried lightly rubbing a cone shaped stone in the guide, but didn't seem to help. Zap it with a countersink bit to bevel the ends?
I got a valve guide dingleberry but don't want to open them up too much.
This was a good excuse to replace my 40 year old Craftsman 1" micrometer with a Mitutoyo and get one of their baby snap gauges. I do enjoy any excuse to buy tools.
These are fresh Edelbrock heads.

 

The best way is to get reamer of the appropriate size and run it through from the side that isn't mushroomed.

 

I would agree, especially dealing with aluminum.