1965 engine code decipher

You can drop in a hydraulic with new lifters. No other change from a solid lifter 'cept the pushrods. But there really is no reason to go hydro on this motor as it already has mechanical rockers and the idle quality and sound from the factory mechanical cam is very docile. Adjusting valves is a 1 year event (maybe) and its is simple. I had a stock 65 S 273-4 with an auto and power steering (!) and it ran like a dream...even on its polyglass tires.