Here is a length comparison of the Leupold 3x, note the available mounting surface between the scopes:
From left: Zeiss Conquest 1.8-5.5; Trijicon Accupoint 3-9; Leupold 2.5-8x; Leupold M8 3x
Here is a Leupold 3x compared to a Weaver K3
Leupold 3x on a Ruger 77 458 Win Mag:
Leupold 3x on a McMillan stocked pre-64 Model 70: note how low the scope can be mounted with its small objective bell:
Leupold 3x's on Ruger #1's in 7x57 and 450/400 Nitro Express 3"