I would test out a pinned joint before committing. If your jig is not rigid enough there is a chance you'll throw the mitre off inside the lug when you drill for the pin. I've tried it and was disappointed to see a gap when I cut the joint up. Brazing looks great, well done.
I would not overthink alignment unless you have a reliable method to inspect it. What I like to do is braze the HT/TT then add the ST so I can check for twist. Then add the DT and BB and check BB alignment.