Got a 75 Gran Fury Coupe, been offered matching rims, 18x9 5.25 backspace & 17x7 4.25 backspace. Anyone know if they will fit? Many thanks, Maxwell

 

17x7 front is not unreasonable
But an 18x9 in the rear of the '75 Fury may take a bit of sheet metal massaging.
Hang a plumb-bob from the center of the wheel well opening and make a measurement to the mounting surface for the wheel. (face of drum)

now measure the distance from the drum face to the nearest obstacle in the rear. Add these two measurements together.

remember 18x9 means that the wheelis 9" on the inside flange dimension. The outside is wider than 9"