I think I have the same mounting plate as you do, but I have a narrow track CJ. Anyway, I welded 1/4" angle iron on the outside of my frame rails and drilled holes through them to bolt the plate to. I winched several vehicles and skidded 2 cords of oak with it and it held. My welding skills leave allot to be desired, but they didn't crack.
1979 CJ5 360 V8 w/Holley 470 Truck Avenger, HEI Ignition, Livewires w/E3 Sparkplugs, Hedman Hedders, Flowmasters, DANA 30 w/Auzzie Locker, AMC 20 limited slip "N" 3:54's, Tuff Country 2.5" lift, Rancho RS5118, Rubicon Express Quick Disconnects, Currie 1/2" lift Heavy Duty Greasable Shackles, DANA 20, T150, Mile Marker PE8000 w/MiFi Controll Box, Bestop Super Top, Warn 6 bolt Premiums, 31x10.50x15