Geoff is right on with his post. I built a back bumper for my 98TJ just because I wanted to and later decided to build a swingout. I bought the spindle, drilled & welded it in.We're going to sell bumpers with a tire carrier on them, so we've been working on these things. I'm NOT saying this to get you to buy ours (which aren't out yet, anyway), just sharing:
We had to add a LOT of reinforcement to the corner where the carrier rests. The weight from a big tire is a lot, and when it's leveraged weight, sitting out on the end of a bar, then it's a tremendous amount of stress and weight.
It can really tear up welds and joints, and you're going to want to "overbuild" it.
Same thing for the pivot point. Most use some sort of truck axle or kingpin type thing. It needs to be strong.
I've never paid much attention to the stock bumper, but it may be worth getting an aftermarket bumper to build on: you may have more metal to work with.