There are 4 things to consider in seal fit of pump to TS cover. oil pump/crankcase wispy gasket, shim under pump nipple, thickness of pump nipple and thickness of TS cover gasket. Here's the recommended combo for all Norton twins below.
Walridge Motors catalog:
Note - Later, thicker Commando type timing cover gasket [06-1092] is recommended for use on all 500-850 twins, but MUST be used in conjunction with oil pump gasket 06-2447 to ensure correct positioning of the oil pump vs timing cover.
Timing Cover all yrs, p/n 06-1092
Oil Pump all yrs, p/n 06-2447
Oil Junction block all yrs p/n 03-2044