Apologies if I've missed it, calipers are of little use in checking drum concentric's relative to the spindle, better to clamp the spindle in a vice with the wheel horizontal and use a dial gauge on the inner drum. I find truing the drum via spokes from about a 'loose' 5Ibft all round usually gets the drum within a couple of thou, and that's probably as good as it gets until the shoes bed in. Though some drums are so far out as to require unreasonable tension to true up. This always happens on the open drum side that has less reinforcement, so it's best to check the drum at top and bottom. It's also easy to go wrong and not run shoes in, once glazed they tend not to conform to any deviation. Another symptom which is compounded by any drum run-out is the fork to hub retention; This will tend to oscillate causing chattering and pulsing, amplifying that characteristic lurch. As this happens under load, it can be tested on the machine by applying the rear brake before the front. If the drums out, the chattering will reduce using this test.