On the top frames there is evidence I have seen on the ones I have investigated that they were painted while partially assembled.
The large bushings between the rear and intermediate side rails (main pivot point above the 1/4 window) often show black paint on one side, shadowing/bare on the other.
It appears many fasteners and pins, washers, clips were phosphate and oil. No overspray and paint on many (latch screws and header adjusting parts come to mind). The bows appear to have been done separately too, as most I have seen have paint under the bracket to attach to the frame. The latch assembly (handle lever arm and latching cam/hook) was definitely painted in pieces, then assembled and installed. The rear frame mounts mostly show bare metal below the bolted plate, painted bolts, which is odd as it would mean they were painted assembled and the cylinder's were in, or they were then taken apart and reattached to install the cylinders.
Would agree with Tim that the headers look to be done separately to the rest of the frame and the main body of the frame appears to have been assembled and painted. I would think with the side rail links, latches, cables, coathooks off, at least for 68's as the main hinge often has paint on the main hinge pin and bushings and the overspray/shadow on the rear pivot. Not sure about the balance link but would lean towards it being on the frame for initial paint as most eccentrics show shadowing on the hex nut (paint on top, underside bare) and shadowing for the washer too, as well as many showing bare or poor coverage on the lower backsides near the frame mount.
Different to 66's which appear to have been painted then assembled and the pin head and bushings do not show paint overspray on the few I've seen.
