Dan is (as usual) correct, the broad chord rudder had NOTHING to do with spin recovery. This was Mod H.104, published on 22.1.1951. The preamble states that this was to increase rudder authority during aerobatics and crosswind takeoffs & landings, as well as to reduce the required rudder input during protracted climbs - spin recovery is simply not mentioned. The "new" rudder was either fitted on the production line or retro-fitted to the RAF's active Chipmunk fleet. The large number already earmarked as non effective stock retained their narrow chord rudders, which explains why a large proportion of early Australian Chipmunks had this rudder.
However, given the distinct rumblings emanating from CASA, the situation regarding aerobatics being permitted in non-straked Chipmunks will soon change....