what is "heavy duty frame" '75?

My buddy just picked up a '75 today from the original owner. He got the bill of sale and the buyer paid an extra $29.90 for a "heavy duty frame".
What makes up a heavy duty frame on a '75? Is there really any difference between a standard and heavy duty frame?

The rest of the heavy duty items on the invoice.
HD springs
HD cooling
HD alternator
T18 4-spd

Lots of rust....

Tom

 

Sounds like a nice rig. I'm going to guess that the frame is gusseted or is boxed. Normally intermediates are not boxed, except for up by the engine mount.

 

My bet is it refers to the extra rear crossmember that is sort of a liner for the regular crossmember. Used when Jeep was equipped with drawbar hitch.

 

I have heard mention of straps on top of the frame rails. I think the V8 '75 frame I bought has them. Not sure if that is the Heavy duty frame or not.

 

My '75 with a 304 had no strapping from the factory. Someone may have added it.

 

A strap on the top of the frame would not be factory equipment. The CJ-6 has a strap, and it's on the bottom of the frame, in tension. A strap in top without a strap on the bottom would not be helpful, because most of the force is on the bottom rail, in tension. I've seen strapping on the top and bottom on race cars, but never on the top only.

I'm guessing that the HD frame looks exactly the same as a standard frame, but that the gauge of the metal in the rails is heavier. I vaguely recall something about that.

 

Checked it out closer yesterday and the boxing looks to be the standard front end.
The rear xmbr is single wall - no doubler.
It has big gussets on the rear to the xmbr but I have never seen a '75 before so that might be standard.
Hopefully the wall thickness is what it might have been because the rust has cut it back a lot.
Tom