here in this pic you see the red bracket that mounts the clutch MC mounted under the dash on side of pedal/colum structure.

it does not touch the firewall and the wall needs no support added.

this pic was in reference to the bulkhead connection hole being smaller on 87-93 trucks in some other posts here on moparts when I swaped the 85 cab for a 91 cab with 5 speed.

it is the same size but moved over slightly for the clutch MC