Aha! Builder identified as Michael Scherz, when he was in Arizona.
http://michaelscherz.com/And yes, this rifle is a veteran of at least one African hunt.
Thanks for the clues guys, didn't take too long to track it down after I saw the scope bases & quarter rib on Michael's page, then a phone call confirmed that it is one of his creations. I'm glad I know more about it now!
Regards, Guy