F350 with no overload springs

I'd add overload springs and a sway bar also. But I would go with multi-leaf(probably 3) with maybe a 1300 lb load rating rather than the stock single leaf. The cost of aftermarket multi-leaf springs at a truck spring shop is insignificant and the labor the same. When I had a '99 F250 I added a second stock overload spring and it did very little. Remember that unloaded the overloads aren't in contact and have no effect on the ride. You'll need to extend the overload bump stops also, I used the hockey puck system at a cost of about $16 versus the expensive aftermarket ones.