[bk1000]

I haven’t read all the replies, but whatever you get remember the older cars ran on leaded gas. Unleaded will ruin the engine. You have to add lead to the fuel. That may be increasingly difficult to find also.

[nascarnation]

Or you can pull the head and have hardened valve seats installed. I did this on my 67 Chevy. Pretty much any auto machine shop can handle this, it’s fairly common.

[Yosemitest]

You can buy additive that will replace the lead into todays fuel.
Also some of the rebuild kits will have the capability to allow use of unleaded fuels.

[Clay Moore]

You can always pull the head(s) and have hard seats installed if you cannot get hard seat heads off of a later model engine easier.