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The first SIII bulkhead was up until and including (at least part of) 1972 with two short gutters, series 2a style Inner Ventilator Panel with large bottom flanges, series 2a type internal stiffeners, and the inner vent to door pillars.
1973 had a unique bulkhead with a long gutter, series 2a style Inner ventilator panel with large bottom flanges and series 2/2a type internal stiffeners.
1974 - 1975 bulkheads had a long gutter, series 3 style inner ventilator panel, series 3 type internal stiffeners (the first time the latter two features were on the SIII bulkhead), inner vent to door pillars with exposed holes in internal faces of door pillars. UNF threads throughout.
1975 onwards had the same as 1974 - 1975 but now with a mix of UNF and metric threads.
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