Most modern standard transmission vehicles have lockouts that won't let you engage reverse while it's moving forward. Mythbusters tested this one years ago. If that is not the case with a mid 90s Ranger, then it sounds like you completely wrecked your drivetrain. Once that syncro is engaged, then something's gotta give. What possessed you to put the thing in reverse? They're not 6-speed transmissions. Do you drive a standard 6-speed as well? That would make that more understandable. Open up the rear differential cover and look to see if you knocked gear teeth off the differential. This is messy with gear oil. Be ready for it. If you didn't trash the differential (it'll be pretty obvious), then your transmission is gone.

Another thing you can do is chock the wheels, and climb underneath. Try to turn the drive shaft with the transmission in neutral. It should not move with the weight of the truck on the wheels. If it does, then your rear end is probably destroyed.