Watch out for different wiring (although there may be only LESS wiring, not that it is a different connector or anything).

The earlier radios and the later radios with blue display, look the same but are somewhat different. The design changed in 1991 to accomodate the extra speakers in the dashboard, where previously there weren't any. The whole wiring connector is different for the later models; or at least it is populated by more wires later on. And I think that there is a large change between wiring. At any rate, when I put one of those in a 940 one time (to experiment) it only worked on 2 speakers and that was it. It worked on 4 speakers in the 740 I took it out of (a 1990 model).

I think--and please understand that "think" means I don't warrant any advice I'm giving you--that the radios are interchangeable. The difference might (again; "might") be only that with one radio, there are less functional speaker outputs. The 940 had an optional 8-speaker system, while I think the most you could option in a 740 was 6 speakers. Most 700s between 1991 and 1992, came only with four speaker systems, and the green-faced radio (whatever model that is). Many 940s came with that one as well, leading me to believe that the wiring is interchangeable, but the speaker functionality might not be guaranteed across models. You could always experiment with it, though, since it IS a really easy swap to make.
--
Chris Herbst, near Chicago.