🤔I have what appear to be two NEW early 60s aluminum finned front brake drums (5x5 bolt pattern).  The part number is:. K-H 43734, yet I can find no info on the web about these drums/hubs.  Any help or info appreciated.

I agree with you. I have found very little regarding anything to Kelsey-Hayes brake drums period. I managed to find a .pdf catalog from 1964 but it does not contain the part number you show above. The fun thing is, I can't even find another picture like you show that is remotely similar in shape to yours. This is a toughie.

Thanks for checking...if you run across any info, please let me know.  They are apparently quite rare!

Today that is very true.

No one remakes Kelsey-Hayes parts and K-H itself has been bought out and sold several times in the last 30 or so years. It was bought by Varity out of Toronto. Then Varity merged with Lucas to form LucasVarity.  LucasVarity was bought out by TRW. TRW was then acquired by Northrup Grumman. N-G sold the TRW Automotive business unit (which included the old LucasVarity assets) to the Blackstone Group, a private equity firm. In 2015, TRW Automotive was sold again to ZF Friedrichshafen, a German conglomerate. 

Bottom line is the K-H name has all but disappeared from the modern lexicon. You have quite a rare piece for sure.