even 92 - 96 are physically interchangeable, as long as u get the HVAC ducts from the donor. The only glitch is the speedo. in '92-'96 it is electric, so the easiest way is to get an speedo cable - digital converter (have seen them at around 150). of course this involves a lot of work, but it ends up with an unique mod.
One more thing: assuming you are planing to use all gauges from donor dash, keep in mind that impedance for the fuel level changed in '89 year (correct me if im am wrong). This means that if ya get, say the '90 dash to your 80's bronc, the fuel gauge won't work (it will always show 1/8). To avoid the hassle with the gauge impedance difference, try to get a '87 or '88