don't stop with just replacing the plug wires. Check and/or replace the spark plugs also. Most misfires are caused by the spark plugs themselves. In the last couple yrs. I've gotten a few plugs that for no reason at all didn't last good and when they start acting up the first thing I notice is a backfire out the exhaust when it's cold.
What year 318 timing cover do you have on it? They changed in 70 so 69 and back timing marks won't be right for a 360 cause they never made a 360 till 71. You can identify them easily because 69 and back has the timing indicator block on the pass side where-as 70 and up is on the drivers side.
