The Kippax held 32,000 in the 60s, as a comparison the Kop was 22, 000 while rag arse rovers had the Stretford end at 12,500 (Including 1500 wooden seats at the back).
As to the "Average crowds of 36,000" everyone and their dog knew to add at least another 10 or 15 thousand because of Swales book keeping, in all honesty I have been to games where you literally could not move only to read later there was only 36-38000 at the game, and that never took into account the gate men who would let one pay and six to jump the turnstile ( Had a relation who made a weeks wages at many a match).