I EXTREMELY CONCUR with Jason_25 (hey!) and Robert. The truth is in both of their posts. You put yourself in a higher bracket when you lift in all areas.
I had an open diff'd 3.55, 96 F-150 Eddie Bauer. I was the constant butt of jokes because it was an Eddie Bauer (stock, save panel K&N and 31" BFG Muds). I got the brunt of it from a friend of mine with a '98 F-150, 4inch sus. lift and 33" 16's. I was leading on a trail and warned him previously of a tight turn that we had to navigate and he said "No Problem, I have a better truck than you!". Behind on that turn all I saw was both airbags deploy and almost rolled into a tree, I was laughing so hard at him! He won't tell me to this day what he did. He said "Why didn't you hit it, well since I have the INFERIOR truck, I guess my right foot is better. I think he realized that he was in a lifted truck and could take more risks. I never got stuck in the 5 speed, 302 because of the right foot. I still have yet to be stuck. I don't chance anything, will eventually, I'll have to roll the dice, it's a question of when!
Think long and hard about this before acting, read, read and read some more. Triple check and remember the bigger the tires the more stress on unmodfied components. Axle shafts, Joints, Steering Box (even though Ford has the best rep for this), etc. Do your homework and acquire facts, opinions (good ones) for a few months and go over this with your pop and maybe he lean towards it. Take it seriously and not like a spur of the moment thing and he just might listen and consider it! Good Luck! hope this helps at all!
Jason