In a wild, misguided attempt to return to topic - for a heavy revolver or auto, the rigging needed for 'comfortable' support of an SAA is significant - largely because of both 'shape' and of 'balance'.
Figure out how to do those things, and a big part of the problem is fixed.
Then, there's 'anatomy' - and a big guy - especially a 'round' one, or a barrel-chested one has a serious problem in reaching the piece because of his width and the length of his arms.
That's why crossdraw works better - the bulk of the ribcage works 'with' the weapon to better hide it.
I looked at both rigs you referenced, and the El Paso rig requires a belt on the off-side to help anchor it, as well as one on the strong side - and unless anchored, that rig 'will' flop about and the spring clip requires a 'snapping' movement in order to make the draw.
You can learn it - but the piece is held vertically and the butt does protrude.
That rig's called a 'Half-Breed' and worked great during the time frame, simply because of the clothing worn back then - today, we wear less - and of lesser bulk.
The Mernickle rig isn't 'Old West' by any stretch of the imagination, and if made of parachute shop nylon, I'd swear my Rigger made it, because it's very similar to what I've worn for years - but mine's balanced by spare magazines and cuffs.
Quite honestly - and I'm trying to help, here - I don't think you're going to find an off-the-shelf rig unless you try a bunch of them on - and even then, I think you'll be disappointed.
Good Luck!
Scouts Out!