There have been plenty of Cummins swapped into the earlier trucks without changing the firewall. The core support is different though. On the 96 the engine sits further back in the chassis than the 1st gen trucks do so to get it too fit using the 96 chassis the front wheels wouldn't be centered in the opening or you would need to modify the firewall.


"Follow me the wise man said, but he walked behind"


'92 D250 Club Cab CTD, 47RH conversion, pump tweaks, injectors, rear disc and hydroboost conversion.
'74 W200 Crew Cab 360, NV4500, D44, D60 and NP205 divorced transfer case. Rear disc and hydroboost coming soon!
2019 1500 Long Horn Crew Cab 4WD, 5.7 Hemi.