I'm not sure you can put the bumper alone on the car. In fact, it seems to me that the 90- bumpers are different on the top and wouldn't allow the proper room for the pre-90 headlight assemblies and grille.

What you really need is a front clip from a 90- car. Theheadlight surround plastic on the later 700/900 is different slightly (non-foglight models only) as is the grille. I mean the 90 is one type, 91- are slightly different. It might cut in 1992 as well. Look and you'll see. The bumpers, however, are the same. Also you need the hood. You might as well buy the whole front clip.

The thing is, a good front clip can run $2500. You can get an entire car for that price, even if it is just for the sheet metal. Or you could just drive the car too.
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1992 940 wagon, very low miles
as well as others.