With out a turbo the 6.9 isn't going to hurt anything. I've just bought a 2wd 74 F100 going to put a non turbo 6.9 in it.

 

yea, ive heard that guys get upwards of 25mpg with the 3.9 (4bt) in these trucks... all i can say is.... wow

 

I have a 72 C10 chevy with a 5.9 and a nv4500 with stock spring only lowwerd it 3/4in.
When you put a 460 with a blower and a couple of carbs with AC that will weigh more than the 6.9.I would just put F250 springs the stearing box is the same up too the 1 tons.It will work just fine.

Dale

 

The steering box is the same, but the spindles bearings, tie rods ect... ect is alot lighter duty.

 

On the older 67-72 trucks the F100 & F250 have the same front spring. Are the 73 and up like that?

 

The spring have different load rateing the f250 Supercab are the same as f350 with AC.
I went through this when I put new springs in my truck when I put the perkins in it.

[but the spindles bearings, tie rods ect... ect is alot lighter duty.]

I have put a few 460 and 429 in F100 &F150 and haven't had any front end problems just keep every thing geased good.

 

i am planning to put a 3.9 cummins in mine when the 300 dies . a friend of mine has one in one of thesetrucks and regularly sees 20 mpg empty. and any mods done to a 12 valve can be done to these engines

 

The 3.9's also benefit from the turbo "upgrade" by taking the stock turbo off an early 5.9L which are cheap and easy to find

 

Hell yeah, Do it ! Think of the gas mileage you'll get, do the 3.9L & you can just wave at these guys that have 351's & larger as you pass the fuel station & smile because you're getting more MPG..........lol

 

I did a 6.9 in a '75 F250 highboy. I put over 100K on that setup and never broke any components. Weight is the only issue you have. The engine does not have enough power to really break anything.