I haven't put the bumper back on mine yet to see, but an extension may not be needed. My weight distribution hitch tongue is pretty long.
Here's a shot from the side, if you didn't want that much extension the hitch can be moved forwards up to ~ 3":

 

There is not one out there rated for 10 tons and up! I called and talked to a tech at Buyers Products Company a leader in truck hitch manufacturing and he said that once you get over 16,000 you need to go to a rigid type hitch/ pintle mounted to a hitch plate .I also reached out to a freind that is a Illinois state trooper that works for DOT of Illinois and he too confirmed my findings and he said that they(DOT troopers) are going to look at your CGWR of the tow vehicle and the trailer. If there is not a Tag on truck that they would then go by your truck plate and the trailer plate to see if you need or have a CDL license . He also said that they would not look at the rating on the ball or hitch at a road side stop. He said that if you where in a accident and your trailer passed you up and hit someone then they would go over everything then ball ,hitch,mounts ....

 

i am thinking an extension will be needed. From the roll pan to the back of my bumper is about 8 inches (stock brackets & bumper).

 

I don't know what engine you have in your F-3 but if is a flathead 6 or 8 you probably will not be hauling 5,000 lbs on the highway? Since your truck's frame is pretty rugged and accessible you might want to try bolting this to your crssmember. At only $14.50 it should be worth a try. Kitts is right down 8 Mile Rd from me and that hitch looks well made and pretty solid.

http://kittstools.securesites.net/store/product4844.html

 

That receiver is meant to be bolted to the bottom of a step bumper not to a crossmember.

 

True . . . But couldn't his F-3 rear crossmember be easily reinforced if necessary at a lot less cost and weight?

 

Depends on what he is planning on towing and how strict the DOT is where he lives. If I was towing a $10K enclosed trailer with a $30K car inside, I wouldn't take a chance on an insurance claim being denied because I saved a few bucks on a hitch.

 

OK. But I'm sure that you are not hauling 10K on the highway with a flathead? This simple but strong hitch should work for anything that a flathead will pull.

 

Not weight, $$$$, and no flathead. My enclosed car hauler was worth 10K alone and the car inside 30K. The hauling capacity of the trailer was 7K# gross.

 

AX, can you give a measurement from the pan to the end of the reciever?.

 

When I built the bed for my truck I replaced the sheetmetal sill (crossmember under the tailgate) with a length of 2x4 0.125 wall box steel. I knew that someday I may want to install a hitch and this would become a structural member of that system. I would think that it would be possible to retrofit a bed with a box steel sill without too much trouble. It sure makes it easier to install the hitch with this in place...not to mention the added strength just in case someone decides to plow into the rear of your truck.