Understand that when a gas block is produced, the receiver side (back) screw channel is through drilled to create the gas port channel in it first, then the lower channel is threaded for the for the that back screw.

On the barrel side, if the bottom of the barrel is dented for gas block set screw, that done by taking messurement  the dead center of gas port in the barrel, flipping the barrel 180, to drill that detent.  This way, not matter what gas block is in play, the back detent screw in the gas block, will always align the gas port to the center of the barrel gas port.

As for other gas blocks, alignment is always gas passage to barrel gas block, and with some gas blocks spaced for front hand gaurd clip, and some not, may end up with the new gas block always having a space from the back of it, to the barrel shoulder.


As for say a gas block that is cross pinned, or even a FSB that is cross taper pinned, then are done per barrel and gas block, and not so much to a give spec.  Simply, if you remove a FSB, and go to replace it with a new FSB, then you have to drill the FSB cross pin channels to match the barrels taper pin channels.  If you did get a FSB from another barrel, than back that the cross pin channels in it, are not going to match the different barrel you are trying to put it on.

So in regards to this on a different barrel,


If new barrel is already bottom rear detent'd for gas block, then not a problem, since as stated, gas block will align since rear set screw is going too index is correctly.  If barrel is not detented, then will need to measure off the barrel shoulder to gas block, then messure gas block from rear to center of its gas passage, to figure out if block need to be tight against barrel shoulder, or not.

As for cross pin in the gas block, bank that it does not match up with the different barrels channel, so gas block channel will need to be used to drill another channel in the barrel.
Note, if gas block has both set screws, then added cross pin is really not needed in the first place. So would just order a gas block that is the correct barrel ID size, as well as the outer size that will work with the float tube in play, and forget all about needing to drill the cross pin channel in it in the end.  With set screws correctly tightened and loctite in place, gas block is not going to move.

Really, the one thing that you need to make sure of, is the new gas blocks ID, is the correct size for the barrels OD at the gas block area.  Hence gas block center channels comes in a few sizes to begin with.

Also, check the upper receiver, against the barrel extension ramping, to make sure they are compatible.

The barrel is dimpled on the shoulder side, so back side and 180 out from the barrel gas port.


As for the gas block, can go with on the one you listed, or about any other gas block that is small enough to fit in our handgards without binding,and correct ID to fit the barrel OD at gas block location.  Hence do not worry about having to install the cross pin, since set screws will hold it in place and shoulder side one will index it correctly to gas port.
If you do want to install the cross pin, then can just use the pin channel in the block once installed, to re-drill the pin slot in the barrel to install the pins.

And again, just the bottom two set screw are enough, and do not need to install the cross pin.

Hence on a DCM rig, so you can adjust the FSB side to side rotation on the barrel to get a dead center rear sight zero, there are only flats on the side of the barrel, not cross pin drilled channels for taper pins, with the FSB mounted to the barrel with set screws both sides of the cross pin channels.


So if these four side set screws hold the FSB in place without problems on a DCM rig, then the two bottom set screws with one of them in the detent, making the hold point to the barrel a lot stronger,  will not have problems as well.  

Hence never understood the cross pin with set screws in the first place on gas blocks, since just make removing the Gas block later a lot harder.  Myself, see it more like a factory pin install kind of thing, to tell if someone did remove the block after it was installed, to void warrenty by end user removing the block after the fact.