Wow!
That looks nice!
One thing that I did was to "tack-weld" the throttle shaft to the bell crank.
As you know - the Offy linkage uses two small set screws (and an expanding pin that you are supposed to install by drilling a hole).
http://dk.favorofareply.com/other/dart/ ... rt_017.jpg
I'm leery of drilling anything that already has such a small diameter (i.e. - the throttle shaft). So what I did was I went to the folks that installed my exhaust, and for FREE they used a mig (or tig?) welder and put a little "tack" to hold the bell crank to the throttle shaft.
The only caveat would be to make sure you have your throttle set up the way you want it - since this is fairly permanent!
One other thing that I did was to install a secondary throttle return spring - both for safety, and also to make sure that any slack in the linkage does not prevent the throttles from closing all the way.
I put the spring on the throttle arm of the "back" carburator - and just hooked it to the threaded hole in the head (between the last two valve cover bolts). I have BBSs - so you might have to do it in a different way.