I'm not 100% sure, but I believe that at 90k miles it would be out of the coverage. So you would need to watch it like a hawk. That would make me too anxious to take it long distances. It could happen at any time, or it might not happen at all. The 5.4L that the 5.0L replaced was a ticking time bomb of cam phasers the same way. When I was searching I avoided that engine for the same worry that would always nag me. Avoided the early 3.5L EB for similar reasons.
I have the 5.5ft box. Personally I don't see the need for the longer bed. This is my first truck and its already hard enough to park and get through the curves of drive thrus. I would not want any extra length. The back seats of the super crew fold up and leave you a huge flat floored cavern to store things. It's like a double car trunk because it goes all the way to the roof. No worries about things getting wet or blowing out on the highway. (If you don't need the seats for people) The F150s don't have great payload capacity anyway. If I had a canoe or long kayak, I would get a hitch mounted bed extender for $50 (with coupon). It disassembles and can be stored behind the back seat so you always have it. Toss a vinyl roll up tonneau and call it a day. Always set for just about anything that may come up.
Tyger Auto T1 Soft Roll Up Truck... https://www.amazon.com/dp/B01LYB4VUD?ref=ppx_pop_mob_ap_share
Price was right for my 9 year old truck. Install was straightforward and I’m happy with the look.