Your going to have to transplant the PCM system also and try to transplant the transmission also. The transmission on your 85 will not me electronically controlled like the one that the Suburban that the vortec came from.
You can keep the mechanical transmission with your Vortec, but your going to have to fine tune it with the Engine's PCM program for the best performance and to keep it from burning up.
I'm assuming your 1985 is carbureted? If you live in an area where there is no emissions tests, you can take the fuel injection off the vortec and place a carbureted fuel system on there if you want to make an ez transition. You will be able to retain your current transmission with that setup. You will need an intake for the vortec heads.