Ok, so got into kind of an argument this evening. Synthetic oil or not in a 1964 318 motor. I was argued to not. I say yes and have used it for years, well Castrol half synth. Been putting it in for the past 20 years and have this NOT well taken care of engine running tops. Pulled the intake to decarbonize 4 years ago, eek a mess. She starts and runs....purrs like shes new. Ton of miles. I use this truck as a plow in my Montana winters, 30 below at times. Starts so well with the synth oil. I would be sure its not a harm to this machine right. What is your input guys. I've always used Castrol 5/30 and WIX filters. Thanks for the input.