360 magnum to 318 magnum swap in a 95 ram

i have 2 issues with my truck, first it idles rough, and second at 75-85 kmph, it stumbles/misses,only under very light accel,and then clears up after 85kmph. i have replaced the fuel pump,cap,rotor,wires,plugs,iac sensor. the truck has a aftermarket propane system on it. there is a black box that ties into the factory harness,its for switching from propane to gas,truck will not run with it unpluged. also it will not idle on propane. has anyone had these issues?
i do have a 94 318 magnum complete with harness,flexplate,torque converter,everything. i wanna put the 318 into my truck,its a 360 magnum . will the 318 drop in with minor changes? and will it bolt up to the bellhousing?

i have 2 issues with my truck, first it idles rough, and second at 75-85 kmph, it stumbles/misses,only under very light accel,and then clears up after 85kmph. i have replaced the fuel pump,cap,rotor,wires,plugs,iac sensor. the truck has a aftermarket propane system on it. there is a black box that ties into the factory harness,its for switching from propane to gas,truck will not run with it unpluged. also it will not idle on propane. has anyone had these issues?
i do have a 94 318 magnum complete with harness,flexplate,torque converter,everything. i wanna put the 318 into my truck,its a 360 magnum . will the 318 drop in with minor changes? and will it bolt up to the bellhousing?