theres several ways to do this, but there isnt much benefit to switching to a L motor since the rods are junk anyway.
i would build your current motor or just build another motor while you can still drive your truck and just sell your motor once you want to do the swap.
switching to the 4r100 is a HUGE task if you have a 4x4, because you will have to change pretty much everything. you will need a new computer, harness, transmission crossmember, different driveshafts, etc.
i would just build up your 4r70 and call it a day.
and X2 on tarajerame and twinscrewed said
2001 F150 5.4 ext. cab 4X4, 5" RCD susp. lift, PA body lift, 35" Toyo M/T's, 20x10 Fuel Hostages, SCT Livewire,
Ford Lightning Supercharger Swap @ 8psi Tuned by JLP, Custom E-fan setup
Built 4R70W by Darrin at BC automotive with Circle D 2400 stall converter
4.88 YUKON gears and DETROIT locker.