The Williams flipper bracket was a 'U' shape, with fixed end stop, when first introduced on Firepower. At a service technicians seminar in the 90's, Mr Cahill who presented these for Williams related how a long-running issue of flipper links breaking was cured by making the stop (by then a detachable item) slightly longer - the defence 'but we've been using it like this for years' was countered by "and links have been breaking for years". There were still some brand new original type brackets in stock at work, and I used up a couple (and gained a couple of new type left sided ones) by fitting them to the ball lock/dispenser mechanism on our Funhouses. The fixed low-height EoS switch attachments didn't matter for that.
Mr. Cahill also mentioned that only the original type fixed end-stop brackets would fit on the upper playfields of the two-level games. Seeing how tightly packed the playfield of Jungle Lord is, I understand what he meant.