valve seats

In classic cars how can I tell if the engine is non hardened or hardened valve seats ?

Nice to know what engines, but if they were replaced with hardened seats, usually only the exh., you can see the replacement seat when inspecting the head. Some engines had flame hardened seats when new, but rare and a valve job can remove this hardening.

All US and Canadian - made cars, (and virtually all imported cars) 1971 and newer had hardened valve seats so they could use low-lead or unleaded fuel.

Before 1971, assume no American made cars had them, unless, as noted above, they were installed later. In my experience, it was pretty rare for owners to pay for this extra feature, so the only way to know for sure is to remove the head and inspect it.

Some pre-71 imports, especially those with aluminum heads had them,

Correct Magic. 51-58 Chrys. Hemi's had steel insert exhaust seats, probably the only older engines built this way.

I have heard that some much older auto, industrial and farm equipment engines had inserts too, because at the time of their manufacture they were intended to run on low - grade (pre WWII) gasoline which did not have tetra ethyl lead.

Of course it's unlikely any of us will actually see one, much less own one.