If I have a barrel which has had an A2 FSB/Gas Block installed, and want to replace it with a YHM gas block, will it still work even though the barrel has been drilled for the original FSB's taper pins? Does anyone have experience with YHM's gas blocks?

Just as a reference, here is the picture of the gas block in question.

As you can see, the set screws are not meant to bind against the barrel itself, and that suggests to me that it will be compatible as a replacement gas block regardless of whether or not the barrel has been drilled for taper pins.

Yes.  No problems.

I just ordered a Bushmaster Superlight barrel from PK Firearms and had them install that very same gas block.  They did a wonderful job and were very fast.  (Ordered on Monday, received on Thursday.)  You might see a ring where the previous FSB was.  Other than that, the Yankee Hill will cover where the taper pins once were.  

Shoots great, no problems.  

it should cover the slots for the taper pin and some brand barrels arent park'd under the fsb so there might be the unfinished area showing.

Update and bump. I've purchased this gas block. The YHM manual says that I should use a specific loctite bonding agent (not the threadlocker, a metal-on-metal agent) on some of their gas blocks, but it's vague on which ones. Does this one require a bonding agent? Should I use one?

Quoted: Update and bump. I've purchased this gas block. The YHM manual says that I should use a specific loctite bonding agent (not the threadlocker, a metal-on-metal agent) on some of their gas blocks, but it's vague on which ones. Does this one require a bonding agent? Should I use one?

Loctite is not required.  If you choose to use it, you can use the threadlocker.  It is a bonding agent with an expoxy base.  It just doesnt hole up to heat all that well.  I still used it on my threads for my FSB.