I would NOT apply clear with a roller or a brush!!! The chances it will look worse than the current finish is very high.
The prep prior to clear coating would be acactly the same ( spray vs roller/brush) and accounts for 70-80 % of the cost and work. If cost and equipment is the issue ......do all the prep and have someone spray the clear.
Words to live by!
Take it to a local detailer and have them take a look at it. They nay not be as expensive as the ckear coat and will do a better job!
The paints used back in the day didn't have clear so they needed buffing to keep the shine. It's part of owning a truck that doesn't need paint today because it's still really a nice truck.
