The Rich Johnson mount usually ends up with the bottom sitting on the weld flange. (i.e. all the way down). But make your own measurements just to be sure. Bolt all the pieces onto the motor, then measure from the engine tin to the flat portion of the mount. Disassemble everything then use your measurement to approximate the location on the body to weld the mount. As Andy mentioned, the engine
tin should sit lower than the engine
shelf by about 0.5" - 1".
A level is handy, but make sure to level the chassis before you use a level on the mount. Also it's helpful to mark the center of the mount. There is a small metal tab that holds a brake line seen in the red picture below which is welded in the center of the chassis. You can use that for centering, plus measuring from the two stiffening ribs on either side of the mount.