At "16.5lbs max", an L hung angle bracket for strength seems like a good idea and looks simple enough. It doesn't even need to sit flat to the bottom, just provide more support the outer edge of the shelf (angle brackets have an inside curve at their bend than may require the bend to sit slightly lower than the bottom edge/corner of the shelf reaching up (<45°)..as that is usually sharp there and would be a pita to round off to match the bracket flush. Better brackets (vs Stanley) would have a slightly sharper bend; but I dindo know a public supplier.
Three engines alone could easily hit that 16.5lbs
Proper wall anchoring too. ( I don't use wedge anchors alone. The top faster is "spring wings" at least, but the best* are metal anchors that when tightened collapse the cage forming backing legs behind the wall (when your not screwing into wall studs of course)) It leaves a threaded anchor for a machine screw that can survive near countless removals. (An old anchor can be punched into the wall or hole sawed around then pushed in and plugged for any "remodels" requiring removal?. I like these because of higher thread count and seemingly better grade of threaded metal than spring toggles.
You must find your approx. wall thickness to avoiding looseness from too long a shank shoulder. It is key to useing them.
*The best for hollow areas IMO.