Just so happens I know a thing or twenty about these types of blowers.
IMO on a stock 4.0L you'd be smarter to fit a centrifugal type of blower.
Mounting would be easier, you could keep the motor all stock, and most importantly you could intercool the charge easier.
Now on top of just plain ease of installation.. the 4.0L is a short stroke motor. Adding a roots type blower gives tremdous low rpm (and instant) boost. Thats generally not good for the drivetrain unless it's strengthened to handle it. Where as a centrifugal type of blower will increase boost/power as the motor climbs in rpms. From an engine standpoint, this is easier on the rod bearings, pistons, and rods.
Personally, if I were gonna do a ranger I'd go with a procharger, intercooler, 9-10psi, a completely new fuel system upgrade, equal length headers, no cats, and a very good dyno tune on a "mustang" dyno.
Do those and it'll live as well as run circles around a non intercooled 5-6 psi roots setup.