If you have a 1970 model with the original motor I would suggest to check cylinders for scoring and take the head apart, new valve seals, check the valve guides, of course all cleaning and lap the valves. Make surre to keep all the valvetrain components in order! so they go back into the exact same location where they came out of. Bottom ends on theses motors are VERY stout. What is the production month?
Enno
Enno