well hopefully people with supras help you out from experience
in general - with same stud pattern:
same:
if the wheel is the an equal rim/tyre combo then it is the same overall diameter so its a match.
if it is the same width wheel and the offset is the same, then you are in luck.
different:
but in different width wheels the offset changes to keep the backspace the same, so the wheel is wider on the road side of the hub. the offset is measured from the centre of the wheel to the mounting face of the hub so thats why the offset changes on wider wheels.
does the rim tyre combo (ie plus size fitment) the same as stock tyre overall diameter or close?
ask him how much backspace it has or you can work out the backspace from the measurements he gave you, then go measure some stockers and see if they are the same or very close. then you will know if they clear the inside (strut, suspension etc)
then you gotta see if they will clear the other side, ie guard side, which can be guestimated or trial fitted if they already pass on the backspace test.
no offense but i agree with norbie about trispokes