I've only done some tinkering and testing around the house and never carried a converted pack... But I've added aluminum stays to a few frameless packs. How much support you need depends on the load you need to carry, but if the pack has a hipbelt the most important thing is to attach the stays to the hipbelt as well as you can.
You could also add a carbon fiber framesheet, with or without stays- I've seen a write-up here on someone who did just that.
That said, it'd probably be cheaper to buy a new or used second hand GoLite, ULA, or Granite Gear pack from someone here- probably would cost you less in time and materials.