I don't know about the new ARB bumpers, but the old ones allowed the bumper to be partially secured with just two bolts, sliding the bumper out to the furthest holes in the frame which allowed a Warn M10000 to just sneak in place. Once the winch got in its spot, the heavy bumper with winch could then be slid backwards into its proper mounting position and all the bolts inserted.
The bumper even without the winch in it is very heavy. If you're strong you can heave it up into position by yourself. If you've got doubts, get a friend to help. Same with the winch. The bumper with winch combo is SUPER heavy.
I'd test fit the bumper by itself before attempting to install the winch. I found mounting the bumper was way easier if I applied a little grease to the friction sliding spots on the frame.
I eventually replaced all the mounting bolts with stainless steel bolts & nuts. After a few years they start to rust (outside vehicle near the beach).