The transfer spring (D12) on the brake clutch (D6) has a little tab that fits into the slot on the clutch sleeve (D3). Check to see if the tab is snapped off. Also, old grease will cause these parts to stick and not function properly causing what you described. And as far as the discs, I think the assembled thickness of the stack is 3/4" (I think=need to check for sure) with a round disc on both ends. The reason I use the total thickness is that there are different sets of discs (early style used more thin discs, later replacements used fewer thicker discs) with a different number of round and keyed. Regardless, round discs at ends.
The noise you hear indicates that the either the hub was not assembled correctly (discs not all the way down into the hub with last lock disc not in slots) or the discs at the ends are dry and the keyed discs are squealing and you may wear off the lock tabs. Look closely at the pictures on the link, take everything back apart, inspect the ends of the disc pack, replace discs if necessary, put a thin layer of grease on each disc, some oil in the hub along the slots for the disc, assemble and make sure axle assembly with discs is all of the way down into the hub, squirt a couple of drops of oil into the filler, spin the wheel and tilt from side to side to spread the oil around a little in the hub and try it again. Good luck...
