There is nothing wrong with a Muncie trans especially the M-22. I assume you know how to shift. I've had a few of them and never replaced a clutch, transmission part, anything. You just have to know what you are doing.
I think he means strength-wise. Behind a mostly-stock engine it probably works fine but if you're making serious torque then it'll blow up more easily than an A-833.
What kept me away from Chevies is the fact that everybody has one, everybody knows what they are, and their engine and suspension technology was wayyy behind Chrysler's back in the muscle era. Plus, look at the experimental research that Chrysler did at the time; ram-induction, 4-valve-chamber heads (DOHC NASCAR Hemi, anyone?), torsion bar suspension/asymmetrical rear leaves, the legendary TorqueFlite, unibody cars weighing hundreds of pounds less and being WAY more rigid than comparative Ford and GM cars... The list goes on and on. I'll be the first to admit that Chrysler build quality sucked, but 40 years later when most of the old Mopars people are driving are either restored or modified, how well a door panel is attached to a door doesn't matter that much.
And for what it's worth, I think my Duster is more slender-looking and "swoopier" than a Nova. And it's longer, wider, and lighter.