bmtrnavsky:
The '39' on the wheel indicated the offset (more/less 1.5"). If you don't run spacers, the track will be decreased by that much (Stock Ranger wheels are either 0 or 6mm (1/4"). Which causes issues with wheels contacting body parts...
You may also find the center cap rides again the front spindle cover.
IMNSHO: Spacers either need to be very thin (6mm or less), so there are still enough threads left on original studs. Or >1", so they are thick enough that the wheel doesn't sit on the original studs/you don't have to cut the original studs/there is enough material in the spacer to support the studs. 2nd, install the studs by hand, ensuring they seat firm against axle hub; locktite the nuts to original studs, and torque to spec.
I would have went with:
https://www.amazon.com/TUPARTS-5x4-5-Hubcentric-5x114-3mm-Compatible/dp/B07VDHJ73K/ref=au_as_r?_encoding=UTF8&Make=Ford|54&Model=Ranger|696&Year=1998|1998&ie=UTF8&n=15684181&newVehicle=1&s=automotive&vehicleId=1&vehicleType=automotive
Aside: Everything I find for Mustang rims says they should have the same 70.5mm center bore as my Ranger (My kids are forever 'borrrowing' my wheels went their rims need new rubber; but what are Dad's for...)
While I would prefer not to run spacers, 99% of the issues I have seen with them have been result of incorrect installation - too many shops rattle wheels on with impact with no regard for proper torque. If the studs are failed before the truck is lowered off the hoist, it isn't the spacer's fault if it fails. (My soapbox).
racsan:
The "trend" was started with front wheel drive cars - in order to minimize torque steer, you need to get the steering joint as close to the tire centerline as possible - the more positive offset on the wheel the easier it is. Then guys in the wind tunnel realized that flush wheel, "Moonies" on streamlines being the extreme, improve mileage by a point or 2, so it was applied universally.
Don't like them on my new F-150. Too many rocks wanting to give my wheels curb rash when I off road...