I have a extra 186 head laying around and was wondering if there is a way to just look at the valve seat and tell if it has been hardened? I have another set of 186's that are ported and polished and I was going to go ahead and port and polish this extra one so I have a spare head (never know). The guy I bought the set from said they had hardened seats but I would like to be able to check for my self.

 

If it has had exhaust seat inserts put in it, then it is ok with unleaded gas.
It is very unlikely that it has hardened seats because they were only made in '69 and '70. The hardened seats made their debut in 1971 in stock heads and are easy to spot.
...They are swimming around in big 76cc chambers. (74cc for 307s)
The 492's are the only ones I know of that were produced after '71, had the small combustion chamber, and may have hardened seats.
So the general rule of thumb for early stock heads:
1.small chamber, leaded gas, soft seats.
2.big chamber, unleaded gas, hard seats.

 

The factory used induction-hardening, as opposed to inserts.

If they're cleaned up, the seat area will be sort of darkened and blue, for maybe ¼" around the seat.

Otherwise, if somebody else installed replacement seats, they're probably hardened enough for modern fuel.

 

Yeah I am pretty sure the seats have been replaced. I doin't think the previous would have gone through the trouble of a port and polish and having screw in studs and guide plates installed and not have had the seats redone. But I would like a way to be sure. I guess I will take it to the machine shop and see if they can tell?

 

It will look like a piece has been pushed in there. You should be able to see a parting line around the valve area. Get a good close up picture (macro!) if you want, and post it up here for the peanut gallery to comment on