Prado to Ranger Wheels

your talking about a 2nd spare , why don't your try it on the front 1st see if it clears all your suspension parts doesn't hit brake caliper etc and has a similar backspace
the chances of you needing it are slim , are the tyre size the same ?

Prado run 0 or 25Positive offset depending on the exact date and Ranger run a 13 Positive offset so I'd say no

According to this site the wheel nut PCD is the same but the Ranger has an offset of 55 while the Prado is 30.

That means it shoudl clear but will sit wider on the car.

https://www.wheel-size.com/size/ford/ranger/2016/

https://www.wheel-size.com/size/toyota/land-cruiser-prado/2003/

Scruffy.

It is not hard to measure the rim widths and determine the centre of it. Measuring from the inner face of both rim types to their centreline of rim will immediately reveal the offset. Trying to follow the above gobbledy gook of offsets may not help.
Of course "fit check" the rim as advised above as that will ensure you know caliper and hub face compatibility. The rim inner dia should also be considered too, because it may prevent fitting the rim on either front or back or both.
Not many people will know ALL factors and unless aware of all measurements you may have a problem.

the prado spare will stick out an inch further. if it doesn't fit, I have a brand new tyre spare 16 inch thou, you can have for free