Neils,
There are a variety of ways that people paint their Healeys during a frame off restoration.
A popular approach with restorers is to assemble the body panels to the frame, surface and prime the outside, remove the panels, paint the frame, assemble mechanicals to make a running chassis, paint the inside of the panels, refit the panels and paint the outside. Problem areas: masking and avoiding wet sand stains to the wiring harness
I am using a slightly different approach. Fit the panels to the frame, surface and prime the outside, remove the panels, paint the frame and inside of the panels, refit the panels, paint the outside, then reassemble all mechanicals onto the car. Problem areas: must be very careful get the mechanicals installed without scratching or damage to the body.
Another approach is to paint the panels off the car and then reassemble. Problem areas: It is hard to get the shrouds and panels back on and aligned without scratching things. You need to have the extra room to store the panels safely before the reassembly process. Also there are areas such as the shroud rivits that would need to be repainted at the very end.
Hope this helps a bit.
John