If I recall correctly, the old SA System 8 reel is the same as the Hardy Marquis 8/9 which is a 3-5/8" inch reel -not all that big really as far as an 8 weight reel goes.
The Hardy Marquis (and lightweights) are my favorite reels. I use perfects and others, but there's something about these reels that just makes them feel right in my hands -more so than any other reel.
You can certainly use it on your #5 rod and I bet it wont feel too awkward since they're a light reel. I'd probably pass though if you don't intend to get a larger rod.
I imagine this reel would match well with a #7 rod which would probably be nice for fishing streamers in WY as well as for any trips you make in the NW for summer-run steelhead.
If you're not looking to get a larger rod, than I'd probably pass and look to find a reel that's better suited to your rod. My favorite reel for a #5 rod would be the Hardy LRH.