Bloggs, I agree with what you have just posted.
You ask "Do you have a reference for the AoA not being constant at the Max Range Speed for various weights?"
No I don't, probably because no one has made an technical argument that it should be, for a jet. However, figure 7 from the boeing doc you linked to appears to suggest that the heavier situation is indeed at a higher aoa, for max range, although one has to extrapolate a bit. Additionally, the boeing doc makes no reference at all to a jet's max range speed being at constant aoa. Now, having said that, for a piston aircraft that may be true, though I'd have to brush up on my aerodynamics before I made that assertion.
You say you don't get that "optimal long-range cruise Mach number does not vary significantly as gross weight (hence, lift and AOA) changes"
I have to agree with you on that. I consider it significant, everyone has their opinion on what constitutes "significant", I guess.