Your 14" rims are probably 6 1/2" wide, with an ET25 offset, and most of those pre-'86 chassis will not tolerate any larger ET number without having the rims or tires rub on the suspension, often the tierod end, although a lower ET number, down to about ET17, can be tolerated without overstressing the outer wheel bearing. After the mid-'80s, M-B, like most of the European manufacturers, began to switch to wheel bearing designs which required greater positive (inward) offsets to get the wheel centered properly on the bearings; I'm not familiar with the '92 type that you mention, but I'd expect it to have an ET in the 30s.
And now to the real point of my responding: if you find the kind of wheels you want, with the proper offset, and have a set of 14" X 6 1/2" ET 25 that you want to sell cheap, contact
jrbaro@wm.edu!