Long Arc,
I know your environment all too well. The trades are usually left to fend for themselves in commercial building.
Looks like they threw you to the wolves on that 8" line. Sprinkler pipe routes usually get priority but gas pipe welds deserve better consideration than what they gave that line. You would think some prefab could have been done to prevent all 20 welds to be made 1" from the ceiling. Not that the typical mechanical or plumbing contractor cares but the position you were put in probably caused many violations adhering to the WPS and the weld quality definitely suffered because of this. Most likely your only requirement is to pass a pressure test. As a contractor I often was asked to weld out whatever was fit and tacked by the mechanical or plumbing contractors fitters (I use that word generously).
If at all possible I would make the weld uphill root to cap. 6010 1/8" root and flush pass about 90amps. At 12:00 I would weld downhill for a few inches. Then examine the ID and then weld the remainder uphill. The cap can be welded with 7018 1/8" or 3/32". That often depended on where the machine was and what size pipe I was welding. 8" I usually weld with 1/8". At the top I try to run hot and weave slowly and carefully. You can't go far because you have to bend the rod. This is slow and frustrating. Then check with mirror.
If you have a WPS for DH welding you can start at the top and run 6010 or 7010 DH fairly hot and it would be less painful. Welding with mirrors in that position is usually more aggravating than it is worth. Experience with this helps as you can hear and "feel" the weld even though you can't see the puddle. It still isn't easy even if you have lots of experience.
I always carry a straight (die or end) grinder for the spots a side grinder will not reach. You can use a rotary file, stone and wire brush on the grinder.I don't know if that would have even worked for you on the top. Chipping hammer, small file, large file, wire tooth brush (plastic type is flexible) and regular wire brush are all helpful.
There will be difficult and almost impossible welds in your career. The key is knowing how to handle them and also IF they can be welded successfully. Looks like you got it the second time. These hard welds will make you better but don't let them make a habit of abusing you just because you CAN make the welds.