The old address under the address sticker reads:
393 Church Rd, Norhtolt, Middlesex
Norhtolt presumably is Northolt

Wilcox moved from there to Chalfont St.Peter in 1969, and the Chalfont office was closed in November 2020.

The L.W.B. (long wheel base) chassis is, as far as I know, not a factory-original designation, since there only was one single DS420 chassis type.