Cool video moose!
62131, quick answer is 4.
Total production of B-24s was 18,400 (+/- data verys)
Willow Run plant produced nearly half, at 8,685 planes. The first Willow Run B-24 rolled off the assy line Sept 1942, the last one rolled off the line in May 1945. Avarage was 9-10 planes per day. Very impressive!
B-24 Survivors 16 total (+/- pending site info)
2 are airworthy and flying, 1 is possible of flight but has not been in the air in quite a few years.
13 are somewhat intact throughout the world, including the 4 remaining Willow Run built. Most of these are on static display needing total restoration before the possibility of becoming airworthy.