this is why I prefer talking offset vs. backspace. offset is measured from the wheel centerline, backspace, from the inside edge of the wheel.

a typical 7" rim is 8" overall width, an 8" rim is 9" OAW (because the width is measured bead to bead)

so you found you need a 7" rim with 4 3/4" backspace. that would be 3/4" positive offset. so you'd need an 8" wheel with 3/4" positive offset. that would be an 8" rim with 5 1/4" backspace. if you get an 8" rim with the same backspace as the 7" rim, it'll only be 1/4" positive offset, and ALL of the extra 1" width will go to the outside.