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.