Just took some quick and dirty measurements:

Cylinder diameter – widest part
M69 ……. 1.575”
M66-8 …… 1.450”
M19-3 …… 1.459”

Cylinder length
M69 ……. 1.670”
M66-8 …… 1.670”
M19-3 …… 1.677”

Top strap width
M69 ……. .660”
M66-8 …… .665”
M19-3 …… .654”

Top strap depth (not incl sight base channel/mortise)
M69 ……. .211”
M66-8 …… .230”
M19-3 …… .218”

Frame – cyl window vertical
M69 ……. 1.558”
M66-8 …… 1.476”
M19-3 …… 1.474”

Frame – cyl window horiz
M69 ……. 1.827”
M66-8 …… 1.812”
M19-3 …… 1.814”

Barrel/frame junction - width
M69 ……. .880”
M66-8 …… .822”
M19-3 …… .826”

Front of frame – vertical – bottom of front to top of front
M69 ……. 2.370”
M66-8 …… 2.289”
M19-3 …… 2.289”

FWIW

Paul