While I do agree with adsm that the 4bt is a good choice, there is nothing cheap about it. They're expensive to buy, usually $2k +. They can destroy any Ranger trans in a matter of seconds, trans and T case(depends on 2 or 4wd) swap needed. They tip the scales at or above big block weight, which means suspension upgrades just to install it. They are poorly balanced and will shake, rattle, and roll. BUT... the sky is the limit with the power you can make.
If I were to build a diesel Ranger daily driver, I'd use a VW diesel.
I had a 4bt in an Explorer... the front diff couldn't handle it. I was making 5-600 lb-ft of torque. So I pulled it and junked that body. Now it's going supercharged over turbocharged to motivate my '79 F350 supercab, complete with 06+ Superduty axles and suspension.