I ended up doing this tiny little mod after fiddling with the JM Restoration mod and it's files and wanted to search the head types used for the different body weights.

John's Underweight Head and Neck replace all his head types, (it's my preference) so this means you can now have the overweight body type for John to stop looking so anorexic and not suffer the cruelty of Rip Jam Wilton and his obscene double chin that even clips through the neck scarf.

player_three_ms1_head_999 is John's Underweight Head and replaces the other heads (This was because I didn't know what I was doing lol)
999 is underweight,
1000 perfect (so far can't be altered)
1001 overweight
001 is neck for first person

player_three_ms1_head_thin is a beta underweight head, much like the player_three_ms1_head_heavy is a beta overweight

player_zero_head_002 is what I assumed to be Arthur's normal head weight, this is what I used over all the other Arthur heads, so no double chin for the old boah either. (and so what if it messes up first person lol)

Yep this is a ridiculously small "mod", but hey, I didn't like double chin mode for a body type that looked more natural as opposed to "I haven't eaten in 7 years" Rim Minkle in 1907, so I made this.

I only know how to tell ya how to install this via RAMPAGE TRAINER so that's how I'll tell ya.

INSTALL:
\Red Dead Redemption 2\RampageFiles\Models

I should also mention I have no idea what I'm doing, it's all guesswork lol