Three shirts / Two Rockmount & one custom made shirt.

Two Men's Vintage ROCKMOUNT Western Shirt Custom Fit-
Pearl Snap Buttons
Cotton Poly Blend Fabric

Burgundy Size 16.5
Measurements taken laying flat:
Pit to Pit 24.5"
Shoulder to Cuff 25.5"
Underarm seam to cuff 22.25"
Back length from bottom of collar to hem 32"
Wrist 4-1/4"
Waist 25.5"
Across Shoulders: 17.25"

Yellow Size 17.5
Measurements taken laying flat:
Pit to Pit 23.5"
Shoulder to Cuff 25.5"
Underarm seam to cuff 22.25"
Back length from bottom of collar to hem 32"
Wrist 4-1/2"
Waist 23"
Across Shoulders: 18"

Green Size Unknown---This is not labeled Rockmount.  I believe it a custom made shirt.  The seamstress or tailor is unknown.

Measurements taken laying flat:
Pit to Pit 25.5"
Shoulder to Cuff 26-3/4"
Underarm seam to cuff 20.5"
Back length from bottom of collar to hem 30.5" ***Square Tail Shirt
Wrist 5"
Waist 23.75"
Across Shoulders: 19"

I have another solid red color Rockmount shirt listed with more detailed trims. I hope you'll check it out.