Assuming 1997 Ranger.
The 4.0l OHV engine was used from 1990 to 2000 model year, very reliable engine.
They do have weak casting point between valve seats in the heads, any over heating will cause a head to crack.
But as long as cooling system is kept up that won't happen, or if hose should break as long as you pull over and don't run it hot it will be a simple "fix the hose" and off you go.
1997 was last year of 2nd generation('93-'97), 1998 was newer body style, 3rd and last generation(1998-2012)
1997 was the last year of the mechanical Auto hubs, they tended to not engage when they got older, Ford switched to PVH in 1998, which were even worse, and dropped "Auto" hubs altogether in 2001.
If not already changed I would budget for manual locking/unlocking hubs to replace the Auto Hubs if you need to count on 4 wheel drive.
You can clean the Auto Hubs up and get them to work but there are no longer replacement parts available, so a broken piece means no repair.
You have to pull the dash to change the heater core on a '97, so make sure coolant gets changed every 2 years to prevent corrosion or blockages.
Chassis parts tend to go 300k without issues, keep an eye on rear leaf spring hangers, they tend to rust out, but on any pickup not just Rangers.
Manual trans will be the M5OD-R1 used from 1988 to 2012 on Rangers, very reliable, uses ATF not gear oil, keep it full, there are some rubber plugs at the top back of trans that can start to leak, these should be replaced with metal plugs when Clutch is replaced.
Bleeding the clutch system on Rangers is a specialized project, lol, be patient and read up on it.
Automatic in '97 model will be the 4R55E, 4 speed computer controlled, Ford did have its problems with the solenoids inside all it's computer control transmissions, the wires would overheat.
Adding another trans cooler is a very good idea, on any newer automatic, 1980 and up.