Well, here is an update. The heater is in. It got a little crowded in there and the wires are a nest (not caused by the heater, but it didn't help either). I don't know how you fix that without ripping out the harness and going with electric gauges. Heater controls flip down under dash when you want to use the heater. Water to the firewall is through a bulkhead fitting. Fitting should be close to in line with just outside of the passenger valve cover (right where I would run the heater hose.)
Here is what it looks like after I buttoned up the dash.
