FYI (if you care) the quad shocks are a Bronco-only option and are part of the factory tow-pkg for the Bronco. Due to the considerably shorter wheelbase on the Bronco, it needs the extra damping up front when towing a trailer. The F and E series have enough length that they do not need them.

 

The R engine code is 93-95 Lightning only.

 

I also have the HD motor in my 92 E150 conversion van, when it wasn't worn out it would run like a scladed dog. I was able to pull of 0-6 in 7 seconds. It now needs rebuilt pretty bad and has lost alot of power.

 

I have an '91 F250 4x4 which has the HD 351. All the literature I have points the HD designation to vehicles over 8,500 lbs GVWR, and differences in the emission controls. On HD models there are Thermactor air tubes at every exhaust port, as well as the crossover tube in the back of the heads and air injection for the catalytic converter. Upon visual comparision with a '93 351 light duty(F150 4x4) I could see no difference in intake manifolds, and only visible difference in exhaust manifolds was the lack of threaded bosses for Thermactor air on each exh. port.