Big update, the heads are on!
The factory repair manual says to "coat each side of the head gasket with liquid sealer", which I interpreted as copper gasket spray. I've used this stuff on EJ motors, it seems to work just fine. I also used it on the copper sealing rings at the bases of the cylinders...
Another thing the manual mentions is a spacer tool to help torque the bolts that hold the rocker shafts on. I just took apart some EA71 rocker assemblies and borrowed the towers to use as spacers.
I was able to borrow the head alignment tool used when bolting these heads on, you can see it bolts to the coolant crossover flange and holds two of the intake bolt holes in place.
It's starting to look like a real engine! I torqued both heads in steps, the repair manual is pretty vague on what I should actually do. This is the OEM manual, too. It says to tighten in stages before the final torque, so I did 5 pound increments. It went very smoothly! Next is rocker shafts, and I have some NOS parts on their way to continue my assembly.