Most Mopars will tolerate vacuum advance into the fifties.
Rick Ehrenberg/ Mopar Action has covered this repeatedly in the last decade (for carb systems but same methods apply) so if you visit their website and look in the tech archive you should find it.
I've been wondering, since magnums (which is what I'm converting to) don't have knock sensors that I know of, how do you know when you've gone too far? They say if you can hear it, it's already been too far for awhile....
Also, be careful tuning by feel. I've tuned many motorcycles that had huge holes in the torque curve that you could fill in and gain a ton of power, but bike didn't feel as fast, because when it was running out of that hole into clean power, it felt like it was "getting into the cam". If the combo is built right and you get a flat torque curve, it'll feel like it runs right everywhere.
