Well here goes! After talking with Lynn Mobley, and the info in this forum, I am going to mount a Mikuni. I have the resources (machine shop) to build the adapters necessary to make it fit. Lynn says a 25mm is the trick setup. Bultaco calls for a 27mm but Lynn says the 25mm gives better throttle response off idle. I realize Senior Bulto would frown on this conversion but I don't need anymore fives account the bike died.
Now my next question - what can I blame any future fives on? Should have the bike running by the middle of next week - will keep you all posted.