Yes you DO need the shims. Otherwise the diff will float about in the bearings.
Beware- current side cover gaskets are thicker, this means you will need MORE shims.
I suggest you borrow a manual... I've had too many beers tonite to write out precise steps...
Preload on the bearings is .002" for early type, and .005" for the later type (which have `thrust' stamped on one side).

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.
