I personally would use the existing intake system on the newer long block (they are the same), if the older intake is functioning properly. It should swap in correctly. Make sure to check your oil pressure sender to see that it is the same (sender or switch),or swap that, too.
Mixing and matching different year assemblies and parts will cause you a lot more work (mostly wiring) than swapping the entire late EFI system to the older truck. The '85 intake should bolt up and align all of the ports properly on the later EFI head (and vice-versa). That being said, I can only assume that you do not have the entire '92 EFI system to swap in (intake, distributor, ignitor, wiring harness, and computer). In this case you should start by getting a copy of and studying the wiring diagrams for both year models, and seeing if there are any differences in the designs. Identify each of the sensors on the '85 intake, and the corresponding sensors on the '92, so that if the connectors (plugs) are different, you can place the existing sensors in the newer intake (or replace the connectors).
I have a '92 and '93, and when I swapped the '92 engine into the '93, had to use the '93 intake to keep from having to splice in different plugs. Also, When you do ANY engine or system swap or upgrade, WRITE EVERYTHING DOWN! Making notes in the repair manual is a good way to have the info where you need it. It can be an aggravating hassle to try to buy a part for your '85 truck, and it doesn't fit (because that was a part you changed). This is also helpful to any future owner, if you ever decide to part with it.
