The 4.0l OHV and SOHC used the same block so motor mounts and transmission will bolt up
You will need the 4.0l OHV computer and engine wiring harness
I assume Explorer has 5R55E automatic and thats going to be the problem
4.0l OHV came with 5R55E 1997 to 2000(last year for OHV), so you need engine computer from those years
1997-2000 5R55E were a little different than 2001 and up
The newer models had OSS(output shaft speed) sensor, which computer used for shifting and sent this "speed" signal out to speedo and cruise, you lose this "speed signal" with older computer
1997-2000 computer expects external speed signal from a VSS, to be coming in from GEM module, which 2001 Explorers GEM doesn't have
2001 Explorer should have 4WABS which did have a speed signal output already converted for use with older computer and speedometer
Worst case is you would add a Dakota Digital SGE-5E, to rear axle VSS wiring to get an adjustable speed signal for older computer and get speedometer back
4.0l SOHC was rated at 207HP
4.0l OHV was rated at 160HP
So that's about a 25% drop in power, 47HP
IMO, I would swap in a newer, 2005-2011, 4.0l SOHC, plug and play, and these have the newer designed timing chains and tensioners, so very reliable