All hores power ratings in the 70s were way low as gov changed specs on how they were done and hp numbers were then net vs gross--

Your early engine has 2 issues that make it a pending disaster-flat tappets and iron heads with todays un leaded fuel------

Change your setup to a later model roller cam block and put some alum heads on it with hardened seats-----------it'll cost a fortune to reguide /seat your iron heads and they are worthless unless you are dealing with a numbers correct restoration---------