Issue #1) I have a Daniel Defense Barrel, low profile gas block & gas tube.  My barrel has been cerakoted black and I am unable to see the marking on the bottom side of the barrel that allows me to line up the gas block.  Any recommendations on how to ensure I got this correct?

Issue #2) I have a Vltor MUR upper.  The forward assist housing had to come off for cerakoting.  Now, I am unable to find the roll pin to secure it back on.  Additionally, I realized that if whatever I use to secure the assist housing in place, it can't be too long as it can extend into the path of the bolt.  Any options of what I can do here?

http://i34.photobucket.com/albums/d131/SDMF350/IMG_0139_zps2e91376f.jpg

http://i34.photobucket.com/albums/d131/SDMF350/IMG_0140_zpse974a3ba.jpg

AN:  FWIW, I've never used any markings on a barrel to get the GB oriented correctly.  A good calipers to make sure you know where it needs to be fore-and-aft, and some careful eyeball alignment with the port and any ink markings you want to make on the top of the barrel.  It doesn't need to be very complicated, as long as its reasonably close to top dead center. - CW

Yeah, before putting on the gas block, I put a small dab of white out to where it lined up.  From there I just eyeballed it.