Hi guys, sorry for took me so long to join you on this interesting theme
Re N9000A/HB-XMU stretched or not... it was born as standard SA.341G but upgraded to SA.342J during 1982 and probably "stretched" during the process as well.
For both N9000A & N9003A I have: regd 4/78 to UCB Leasing Corporation; leased to Sabine Offshore Service Inc. (operated by Bristow Offshore Helicopters, Inc.)
I also have these Gazelle regs as once operated by Bristow: N3593B, N18842, N47315, N69506 & N9002Z ... but need confirmation of these data!