I am not sure who put those big U bolts in Macca, but I do know they have been there since about 2014 as I was shown those by a instructor from Melbourne prior to running an Army activity up there. I only remember one pair though and him stating they had been replaced around that time. I know the Army used to use that 3 pitch abseil down the North Wall (has done for 20 plus years, they ran some activities while I was there but I was instructing in the water cell) and Commercial groups also use the same one the North Wall. I believe the ones lower down in the cave and the ledge below that were replaced around the same time (it was an old chain one trip and the next new bolts) if my memory serves me correctly.