My 1979 CJ-5 proportioning valve looks like that too. I couldn't easily find anything to support my error-prone memory but I _think_ that 1979 was a cross-over year for disk/drum fronts. Something makes me think it was all drums in `78, optional disk in `79 and all disk fronts by `80, so the difference in the valves might be in the volume differences in the pistons. I think (but could be completely wrong) that the only external difference is that the reset under the rubber cap on the end is a button that needs to be depressed on one version and a pin that needs to be retracted on the other. There _may_ be an ID stamped in the brass, but good luck finding it.
Oh, and the mounting plate that the valve bolts to is a prime site for frame rust. Crap gets down behind the plate and holds it against the inner face of the frame box. You do need the plate, though, since that supports the brake lines.
I'd go with the factory-bent tubing, unless you really enjoy measuring, bending, fitting, bending, fitting, measuring, cursing, scrapping, bending, fitting, bending, fitting, cursing, lathering, rinsing, repeating. When I redid my `79 frame-off I went with stainless tubing, because I wanted to do them only once. Be sure to order new retaining clips since the original ones are either rusted or gone flat. Don't forget that there's a flex hose that runs from the wheel arch crossmember to the rear axle, you'll want to redo that while you're at it.