All--
Thanks for the input (no pun intended) and various suggestions. I went for a short ride again today and while the noise is still there I cannot pin down its sourcem though it does seem to be up coming from around the front of the transmission tunnel. FWIW it does not seem to be related to engine/transmission speed and sounds the same in neutral as at 70 mph.
As I said over on the Healey newsgroup it is possible that my hearing this noise is related to the fact that I have only recently started driving with side curtains on and sliding window closed due to temps, and I might simply be hearing something that has been there for a while.
My feeling is that I am not going to pull either the engine or transmission unless things get noticeably different and if it is a failed transmission bearing, or even a thrust bearing I think it would make itself quite evident as it deteriorates. Then again I will probably be dropping the pan to check out oil pump and main bearings to follow up on the oil pumps inability to prime itself and general decrease in oil pressure (it has been about 50 K since last rebuild) and depending upon what I find the engine may come out for a different reason.
I'll keep an eye/ear on things and definitely post about any changes, etc. Thanks again for all of the feedback and in answer to Bob's question I simply cannot remember what BJ8 clutch I used--in fact I did not know there was more than one.