is it alright to burn unleaded gas in a Plymouth flat head 6-49 model

Yes it is. When your car was built the regular gas was 70 octane or less, with low lead content.

Your engine has hardened valve seat inserts from the factory.

Today's regular unleaded is actually higher octane than the hi test when your car was made.

You can use today's regular gas with no problems.

Thanks Rusty, just wanted to make sure----