Rick,
Please don't attempt to smoke those together, or disaster will be in your future (sad to say). If you run that roast at 235, it will be overcooked and tough. I'm not sure what a "mock tender roast" is, but it's only 3 lbs (remember my steak comment
). If it's a sirloin, it will probably end up gray.
What kind of ribs? Baby back, or spares? Back ribs should only take 4.5-6 hours (depending on your taste for doneness), whereas spares will take 6-7 hours. Seeing you want to eat at 5, I would put the ribs on early enough to be done .5 - 1 hour before dinner time, then wrap them in foil and rest them in the cooler until dinner. I would probably smoke the small roast before the ribs, at 200, until it reaches 128-130 internal temp, then double-wrap in foil and put in the fridge. I would reheat the roast, unwrapped on rack in a pan, in a 200° oven, until the internal temp gets back to 130. Then, remove it and let it rest while the oven gets up as high as it will go. Once the oven is on high, reverse-sear it for 5-8 minutes. The ribs should be resting in the cooler, so all you need to do now is slice the roast and the ribs, and serve!
It is VERY hard to smoke two things that are SO dissimilar, at the same time, and have good luck. Things that smoke at the same temp, like maybe butts and briskets, have a greater chance of success; your two choices do not.