I see no problem with switching from conventional oil to a full synthetic (or back again) You can even mix the 2 together in a pinch.
I believe in regular oil changes and using a quality full synthetic oil and quality filters. Some here say that they change the oil in their SOHC's at 3,000 mile intervals. My opinion is that doing this buys you nothing and wastes your money. Changing your oil every week will not prevent plastic timing chain components from getting brittle and breaking, which is what kills most SOHC engines. Depending on the conditions you drive in (stop and go traffic, dusty conditions, towing) you might want to change your oil at 5,000 mile intervals, rather than Ford's recommended 7,500 miles using a synthetic blend. I use Mobil 1 10W30 Full Synthetic Extended Performance with extended life oil filters in my V8's. They typically only see around 5,000 miles of around-town use (or less) in 12 months, so I change the oil in them once a year. In my one remaining SOHC I used Mobil 1 Full Synthetic 5W30 and changed the oil more often (2-3 times a year) regardless of mileage. The previous owner did not treat this truck to much, if any, maintenance. I could tell this by the amount of sludge in the engine, black transmission fluid and almost no oil in the rear diff (what was there was mixed with water) yet at 200K+ miles it was a head gasket that took it off the road, not the timing chains. And even if the TC plastic pieces haven't broken chains stretch. The longer the chain the more they stretch over time and Fords SOHC engines have a lot of chain in them (both cams, jack shaft, balance shaft in the 4x4's). That's many feet of chain to wear,
