Do these heads have hardened seats?

According to the serial numbers:
The block is a 1979 318 ( 4179730). It is 0.030 over on a 25 year-ago rebuild then was pulled and sat for a long while.
Intake, although it's coming off, is 1967-69 2 barrel (2468960-2)
Heads are 1968-74 (2843675)

Is there a way to tell if the heads have hardened exhaust seats?
The plan was to do some home head porting, possibly put in 1.60 exhaust valves and get a valve job, put in a 4 bbl manifold and carb, and put in a cam.