Trail rated is correct, you want a high ZDDP oil, which is higher in Zinc, an anti-wear additive that is important for the flat tappet cams. API has reduced the ZDDP levels in newer oil because that same additive causes premature wear to the Catalytic Converters. You need to shop for an oil that retains the ZDDP levels. Alot of people choose to use a diesel type oil, but there are many oils on the market with acceptable ZDDP levels.
Here is a TSB from Amsoil explaining it a little better, if you would like to read about it.
Also get a good filter, WIX is a popular quality filter with a good anti drain-back valve. Stay away from Fram!