[69 C10 LWB]

I had a 64 C20 LWB and I swapped the stock single master for a stock dual non power 4 wheel drum master from a 67 or 68. Bolted right in and bore size was the same since both were 4 wheel drum C20s. Youll have to do a little research but I believe 67 or 68 was the last year you could get front drums and the first year for the dual master cylinder. The 64 stopped great and didnt require super human strength on the pedal.