Cooking at those temps, you should of left them in for 2 or 3 more hours. That is a silly low temp range. Meat renders better at higher cooking temps.
With ribs, I'll go first hour at 250ish, then crank up the heat to 300ish till done (pass bend test, toothpick test, or bone tug test). I do this so I get an hour in at a lower temp to get some smoke on the meat, then crank up the heat to power through rest of cook.
When doing ribs like that, spares are usually done in about 4 hours, and loin backs are done in around 3.25 hours or so. IMO, the trick to making a hotter cook work is to keep the cooker closed the whole time. Don't open it for anything till you hear the sizzling start to calm down. You can place your ear close to pit or exhaust and hear the sound the meat is making. No need to peek. When that sound starts to get a bit quieter, they are probably about done, but I'd check at 3.75 hours anyways for spares depending on how meaty they are.
Modded Brinkmann Gourmet. Basic UDS. Rescued 22.5" OTS. SJS Mini-WSM. Stubbs. B&B Oak Lump.
Cannondale 2009 F8 (for burning off all the great BBQ)