Its not a terribly difficult swap, but there are a few things to be
aware of. The trans will basically bolt up to any Smallblock Mopar
engine (318/360 in the 80s) if you use the correctly weighted torque
convertor or flexplate. The 360 is externally balanced and has to have a
weight on the convertor, the 318 does not. People put these
transmissions behind big-block v8s in muscle cars, too, but that
requires an adaptor plate and significant modification.

Beyond that, there's the issue of the crossmember that supports the
tail-shaft. The 4-speed is fatter in the tailshaft area (that's where
the O/D was tacked onto the A-904 to create the A-500, or onto the A-727
to create the A-518). You may also have to massage the floorpan to clear
the fatter tailshaft, although with a ram truck it should be minimal. IT
gets pretty extensive for the folks that put these transmissions in
Darts, Valiants, and Barracudas, less-so for B-bodies, not much
difficulty for C-bodies, and virtually no problem for trucks.

And finally, there's control of the lockup convertor and O/D. In the
vehicles that originally came with an A-518 or A-500, the computer would
engage the locking TC and the O/D at the correct times. You CAN control
both with simple toggle switches that you operate manually, but the
danger is that if you improperly engage lockup or leave it engaged upon
coming to a stop, you can overstress and damage the lockup clutch.
Except for the very heavy-duty versions of the 518 that went behind the
Cummins or the V10, the lockup clutch is not meant to handle a great
deal of torque because the computer always disengages it when a lot of
torque is demanded from the engine. There are aftermarket controllers
intended for retrofitting these transmissions to muscle-cars that work
it all automatically based on throttle position and manifold vacuum, so
it would be best to consider that option.

Its not a terribly difficult swap, but there are a few things to be
aware of. The trans will basically bolt up to any Smallblock Mopar
engine (318/360 in the 80s) if you use the correctly weighted torque
convertor or flexplate. The 360 is externally balanced and has to have a
weight on the convertor, the 318 does not. People put these
transmissions behind big-block v8s in muscle cars, too, but that
requires an adaptor plate and significant modification.

Beyond that, there's the issue of the crossmember that supports the
tail-shaft. The 4-speed is fatter in the tailshaft area (that's where
the O/D was tacked onto the A-904 to create the A-500, or onto the A-727
to create the A-518). You may also have to massage the floorpan to clear
the fatter tailshaft, although with a ram truck it should be minimal. IT
gets pretty extensive for the folks that put these transmissions in
Darts, Valiants, and Barracudas, less-so for B-bodies, not much
difficulty for C-bodies, and virtually no problem for trucks.

And finally, there's control of the lockup convertor and O/D. In the
vehicles that originally came with an A-518 or A-500, the computer would
engage the locking TC and the O/D at the correct times. You CAN control
both with simple toggle switches that you operate manually, but the
danger is that if you improperly engage lockup or leave it engaged upon
coming to a stop, you can overstress and damage the lockup clutch.
Except for the very heavy-duty versions of the 518 that went behind the
Cummins or the V10, the lockup clutch is not meant to handle a great
deal of torque because the computer always disengages it when a lot of
torque is demanded from the engine. There are aftermarket controllers
intended for retrofitting these transmissions to muscle-cars that work
it all automatically based on throttle position and manifold vacuum, so
it would be best to consider that option.