I removed the engine and clutch housing from my 70 and found that when i put it back in the shaft coming from the engine and the shaft coming from the tranny wouldn&#039;t run true together unless i got all the shims back in.  This is a little tricky buy if you take a pry bar and put it in between the clutch housing and engine bay you can flex everything enough to get them in place.  Also, I used a dial indicator and checked the side to side and up and down movement of the shaft coming out of the clutch housing to make sure everything was within specifications and it was.  So, yes it is important to get all the shims back in that were there originally.  Hope this helps.