They can be designed to distribute all their weight to the frame, but it's alot easier to build for a pickup or a 40 than a 4Runner - there's alot of body overhang to deal with, but if you have a sturdy base for the bumper: Generally a 6X4 rectangular 1/4 tube capped at the ends with double frame scab-plates to "sandwich" the each frame rail between the plates. Finally a heavy-duty spindle to mount the swing-arm on.
If your payload's too heavy, then a 90 degree upright off the bumper's corner, heavily trussed, can mount a second spindle for more of a box-frame mount.
as I mentioned, this is much easier on a pickup or 40 than a 4Runner, because the 4R rear frame is boxed off with a rear strut - but it can be done, if you're willing to do some serious restructuring of that crossmember.
It's also worth mentioning that there are two general types of bumper - one for wheeling and crawling - a low-profile affair that is designed not to interfere with the angle of departure.
One for expeditions and light wheeling - these tend to be larger and beefier because everything expedition has to be considerably more idiot proof, and because more concern is given to capacity and ability as opposed to angles of departure, which you'll see: die-hard wheelers will usually pick a tight line because the thrill is in threading the needle. Die-hard expeditioneers will generally take a looser, less risky line - no need to jeopardize your hardware if you have to live off it for a week or more.
I say this because the bumper you'd like to build is leaning more toward the latter, and if your intent is wheeling or crawling, you may want to look into other options.