The 4.6 fits but you may need to lose ac and parts of the firewall for clearance. If you find DOHC 4.6 then the problem becomes worse.
If you have time money and fab skills a 4.6 5.4 6.8 7.3 6.0 are all doable.
You asked for the easy route. Thats the 5.0. FWIW I picked up a 98 Ex for 650. Sold the extra parts off of it and made my money back. I now have a free 5.0.
Also Trucks did this swap check out what they did to get a dohc to fit. Called project rolling thunder.
99 x-cab 4x4 4.0l auto
mods, cranked t-bars, silencer delete, k&n drop in, Rebuilt trans ,Trans Go stage 3 shift kit, 3200stall Fuddle Racing Torque Converter,
VANIR 63mm TB, Roush split rear exit exhuast, E-Fan, JBA Headers
Auto up/down both windows, OHC, EATC (soon to be modded)
03 Crown Victoria Police Interceptor