I am building a .223 AK74 using a virgin barrel from AK-Builder.  I am to the point I need to mount and pin the gas block and the FSB.

I didn't have a problem with the barrel retaining pin.  But the two slots I am asking about are much, much smaller.  

If anyone can offer a link to a tutorial, etc., I would deeply appreciate it.

akfiles.com or youtube will have it.

Do you have access to a mill ?? Best way is to use a 2mm center cutting endmill to make a flat spot on each side of the barrel, then get the shorter "screw-length" drill bits and drill from each side to meet in the middle to insure the bit doesn't "walk" like it could if you try to drill straight thru from one side. Go undersize on the hole and ream for the correct interference fit for the size retaining pins you have.

If you try to just drill it chances are the drill bit will walk away from the rounded surface of the barrel causing problems. Using an endmill to spot the holes reduces the chances of that happening.