There is an Urban Myth, first heard at FSI, that the original 76 didn't have that complex mixing unit. The engineers put together a system that looked like it would work, and all the external airframe designer had to do was create a bulge on the left transmission to accommodate one of the servos, which poked out a bit.
Oh, no, says the designer, the external appearance must be smooth and sleek. Move the servo so it doesn't poke out. So, the servo was moved and that nightmare mixing unit was devised to allow the control runs (already fixed in the design) to still operate.
Makes a nice story, anyway - thanks Eber!