Offset is easy to measure, or match at least.

All you need is two straight pieces of wood or metal that span from edge to edge on the wheel. If the wheel has a tire on it, they must be the proper length. Hold one stick on each side of the rim and use a ruler to find the center between them. You then measure from that center to the mounting surface on the wheel.

If all you want is to see that the wheels match, the exact value does not matter, as long as the wheels have the same measurement from center.

More problematical is the center hole of the wheel. Volvo wheels are "hub centric" that is, the center hole of the wheel holds the wheel in the proper place, hence the need to have the hole made to be the proper size and properly centered in the wheel. Otherwise your wheels will bob up and down like a clown car.

I have a friend that builds hot rods, and he has a listing of wheel compatability. He told me long ago that full-sized Fords have the same bolt circle as Volvo wheels.
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96 855R, 95 855,854, 90 744 Ti - 340,000 Volvo miles put on 7 bricks