The International CBX Owners Association

Im thinking of restoring a '79 and am wondering how hard is it to 'fit' a different swing arm? Ive seen several Cbx's with Gixxer and even a Ducati single sided and am wondering if I want to go down this road, how much am I biting off?

That totally depends on what your goals are. If you just want a better swinger that's more rigid, than a CB1100f unit will work well, look pretty correct, and work with your current shocks. Likewise, a swingarm from the later ProLink bike will work with the addition of some bosses welded to it for the lower shock mounts, and there is a guy by the handle of JJam that specializes in this work. Do a few searches here and you will turn up a few threads where this is explored. If you want one just because it looks kewl or to run a wider tire, there are also options, but details might be scarce. Again, do a few searches, it's all been done.

NobleHops wrote: a guy by the handle of JJam that specializes in this work. .

...here on this site???

One issue you need to consider is the centerstand. If you go with a swingarm that has a bracing, in most cases you will have to give up the centerstand.
Also, the 79 CBX is the only one with a 14mm swingarm axle diameter. For any other swingarm, you need to either drill the frame holes and the footpeg plates (or replace them) or you need a sleeve for the 14mm swingarm axle.
The easiest conversions are the 1100F arm, a Prolink arm modified to twin shock, a Kawasaki Zephyr arm. All need to address the s/a axle diameter.
Ever so often, somebody will offer a custom swingarm made specifically for the 79 CBX (like a CalFab or a Metmachex).
Personally, I do not care much for the single sided swingarm conversions. There are too many secondary issues, like length, wheel alignment and wheel matching with the front.