Please help stop an expensive mistake - rims on '63 5 lug swap

[J1MMY]

I apologise up front for being a bore but the availability of wheels over here is limited and you'd find the price of them hair raising.

I am looking at buying 8x18 4.75 backspace for the front and either the same for the rear or 9x18 5.25" backspace. The truck is lowered 5.5" at the front and 6" at the back. I have measured up and mocked up and am pretty sure that the fronts will tuck in the arches (rolling the lips will help too) but I am unsure about the rear, particularly the 9's.

If anyone has fitted this combo (or part of it) on a fleetside, or is aware of such a combo on a 5 stud converted truck please do chime in. I've gone through as many wheel/tyre and static drop threads as I can.

Thank you.