Eric,
Is your 880 the one with the 350-watt (1966-70), 400-watt (1971-75), 3 amp (1975-80), 4.5 amp (1980-85) or 5.4 amp (1985-87) motor?
In late March 1985, the fan case on this and all Royal metal uprights changed from being all-rounded to partly-angled.
~Ben