After fitting a new oil seal in the timing cover a tip i read is to fit the crankshaft pulley before tightening the cover bolts so the cover and oil seal are aligned around the pulley. Then remove the pulley to tighten the remaining bolts.
This should be done whether a new seal is fitted or not to ensure the pulley is central to the cover and to reduce the risk of any oil leak.
MGB tips mods and maintenance 