Fair enough, Marnix, but it remains a bodge in my view. If secured from slipping with a rubber pad, the jubilee clip would need to be loosened... and tightened afterwards! A quite dangerous and obvious source for things to go wrong.
Front wheel swaps in the early/mid '70s? With 280mm discs and TT100s? Maybe one, two(?), during a 24 hour event. How many mechanics were allowed to work on the bikes during pit stops back then? Three would be required to perform this swiftly, two would be fumbling quite a bit. Not at all sure that fiddling and fumbling with pads in mounted calipers while slotting the wheel back in would be much quicker than removing/replacing the calipers completely.
Their tank-swap strategy, instead of filling up, was probably far more effective, especially before quick-fill dump-type canisters became the norm.
piet