Remember, the old engines from the 1970 burned leaded fuel. You may need to have the heads/valves rebuilt for unleaded fuel. Please read below.
This is not a problem for newer engines, which have been engineered to run on unleaded fuel, but can be troublesome for many of the older engines still out there. While the increased anti-knock properties that lead imparted to gasoline have been addressed with various other additives, the same is not true for lead’s lubricating benefit. Newer engines have been designed to operate without the combustion chamber lubrication that lead provided but older engines are susceptible to certain damage without this lubrication. In particular, the exhaust valves and their seats are vulnerable to accelerated deterioration when an older engine is run on unleaded fuel.
There are two ways to address this problem. The first is with the addition of lead or lead substitute to the fuel in your tank. This creates an ongoing expense and is a little bit of a nuisance but is probably the best solution for cars that are driven infrequently. The second way to deal with the absence of lead is to modify your engine so that it does not require upper cylinder lubrication. This is done with the installation of stainless steel valves and hardened valve seat inserts.