19 weeks later ... a Bridgeport is usable ...
Being compulsively anal I decided to spend time to try to understand the head rattle and see if I could solve it without coughing up $700 for new parts. Turns out if was indeed solvable and now, after tearing the head down more times than I care for, the machine is purring along - no rattle. gib shimmed also so we're now fully operational. Very happy about that - it has been every weekend for 5 months. Phew.
An an FYI, the BP 2J heads can rattle when some parts becomes worn. The two main culprits are the plastic bearings on the cones for the pulley system. I replaced those as part of the H&W rebuild kit. The other reason is the dog teeth engagement when in hi speed. Worn dog teeth mean rattle. Often it goes away under load (when cutting) but it is sure annoying to have a machine that sounds like bolts in a tin when you turn it on. The hi/lo speed lever can be adjusted up to cause the bull-gear and lower dog teeth to get better engagement but sometimes that does work.
Alternatively, you can remove the 'locating pins' that hold the lower head 'tub' onto the bull-gear housing and 'float' it to find a sweet spot where the teeth engage. I did this and it completely removed the noise.
I now have a mill that I am happy with. :-)
Greg.