The "f/8 and be there" rule, for a 35mm lens on a full frame camera is really about the hyperfocal distance and the distance from which everything in your shot will be in focus. So with those settings, one could expect that without having to focus at all, if you're at the right place at the right time, your subject/scene will be in focus, and thus save you time when trying to capture the shot.

Admittedly, you'd probably set your camera in Aperture Priority, Manual Focus, to achieve the same effect (and let the camera decide ISO and Shutter speed for you. Or just the shutter speed if you fix the ISO).

So if I understand your question properly: How do I get the same Hyperfocal distance at 50mm on my camera? Depends on the Camera, since Full Frame/APS-C will give you different hyperfocal distances for the same focal length and aperture.

So look at the DOF Calculator here, enter your camera, focal length, choose an f-stop, and look on the right side for the hyperfocal distance. For example, taking the 5D Mk II, focal length of 35mm, f/8, the hyperfocal distance is written as: 16.9ft.

Same camera, switch to 50mm, the hyperfocal at f/8 is 34ft. To get back at a distance of approx 17ft, play around with the f-stops, and it says: f/16.

And if you take the Olympus E-1, Focal Length 50mm, then the aperture you need to use for a 17ft hyperfocal distance ends up being... f/32.