I've watched the rebuilding process on several clutches, and the balancing procedure is the last thing that gets done after all the reconditioning and assembly is accomplished. At worst, the loss of that balance weight might create an annoying harmonic at a certain RPM, but it won't keep the clutch from functioning. Run it awhile, and see if it shakes too much to suit you. An inline six is naturally balanced, because of the even spacing between power strokes and the design of the crankshaft. It would take a pretty good bit of imbalance on the pressure plate to make things shake very much.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
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