Pete -- I would highly suggest upgrading from the 85 wiring / computer. The 85 setups use a 1 year only computer, and it is far from being totally reliable. it is a very easy upgrade to an 86 ECM, simply needing a `165 ECM, a few relays, and a bit of wiring changes.
You can find details on the swap here:
http://www.eecis.udel.edu/~davis/z28/ecm_swap/
If interested -- I've got a few spare `165 ECMs sitting around here, both work fine. One has a chip, but I am not sure what it is for, so you'd probally want to buy a new chip for the engine you are building. You can have them fairly cheap. I can also include the connectors for you. As far as the relays go, I'd encourage you to use a set of mini-cube relays from Bosch rather than the big nasty looking things a stock TPI car used. They are far cheaper to replace, and are likely more reliable.
You can find them fairly cheap, along with handy connector bases that clip together to space the relays out nicely at
http://www.partsexpress.com/ -- They have excellent prices, regular specials, and good shipping prices. My package arrived in good order, and in very good time.
You can use whichever distributer you wish with the TPI setup -- in cap, or external coil. I've used both, and less a connector change, they are totally interchangeable.
Being an 84, your VSS is very easy to solve. Simply use the signal output from the green boxed optical sensor that is bolted to the back of your speedometer. It has several output pins that send out a 2k ppm signal that the 85 and `165 ECMs need, along with your cruise control.