While your in there, it never hurts to adjust the valves, replace the plug and clean the stock fuel filter and place another external filter on the fuel line,(two-reserve also) And very important is the chain tensioner, often WAY over looked on them. Just tighten the snot out of it, they always come loose and need to be adjusted. I think the two biggest problems are points and chain tension! Oh, and nobody ever changes the oil

I do the oil two or three times a year, cheap, easy, and great insurance on the longevity of a 70. Don't get to caught up on the filter aspect, unless you think the old oil has issues. Its a pain to remove and clean, hence the many oil changes.