GQ, by "roll bar" I assume you mean a chrome roll bar like you see in the bed of a pick-up truck? The Bronco in the movie "Oceans Eleven" had a double-tube roll bar in back, as did the Bronco in "Romancing the Stone". Looks awesome topless!
Or is it one of the factory roll bars that some Broncos came with? Smittybilt offered a roll bar, particulary for 78/79 Broncos, that fit under the cap. I don't know for sure if that will fit in your 84.
Keep in mind that the first roll bar mentioned is only for "looks" or mounting lights, and is not considered a true safety feature in a roll over. It's still better than nothing, though, so if it fits I would get that over the hitch. I plan to install a 10-point roll cage in my 84 Bronco. I have it in the "parts" room, just haven't installed it yet.