Mine also had the 2 bbl intake and I believe the spacers were about 1/4" thick. The heads had the water pump bosses on the ends like the 354/392 car heads but they weren't machined.

Does your engine also have the relocated oiling system on it?

That was another neat feature mine had as well and I was able to use an aftermarket relocation spin filter kit and mount it on the firewall of the car.