There is no visual proof in the linked newsreel to really nail down how high the bar was set.
Better evidence are the photo sequences pubished originally in Life and posted on Browning's website (http://sites.google.com/site/dickbrowningarts/home/life-magazine
) and again at http://books.google.com/books?id=KEgEAAAAMBAJ&q=browning#v=snippet&q=browning&f=false
(scroll to page 69)
Despite the fact that the last word of the Life Mag URL is "false", both series show Browning clearing heights that would have been world or national class HJ marks in the mid-1950's. The latter claims a quite believable looking 6'8" clearance from a surface that appears to be a track venue rather than a spring loaded floor.
So it is not difficult to lend credence to the claims that a two footed flip done by a talented athlete can produce lots of altitude, even in the 1950's. After all, the Jerome Simpson airborne touchdown forward flip by a non-gymnast with several pounds of pads on made every highlight show last fall (you can find it easily on any video search.)
Most interesting to me is Browning's back-to-the-bar clearance form which pre-dated the flop technique by a decade.