Mario's size in Sketch-up when using a scaling of 1
Length = 333'
Width = 333'
Height = 555'
One effect of tunnels using these proportions is that when 
Mario is crawling he will appear above the ground. But 
once you stop crawling he will go back, he can't actually
clip through the ceiling.
Another thing, the camera has a hard time focusing on Mario
while in a tunnel like this.
Notes:
Crawling doesn't actually decrease the height of Mario's hitbox.


Other entities size:
Goomba, Bob-omb, Small koopa, Pink Bob-omb, Boxes(Non-carriable):
333'x333'x333'