Cleaning the engine ends before you put the crank end covers on is a great idea. It's very time consuming to clean these area with the assemblies bolted on. But while they are off it's a very quick process. I parts brush with your degreaser will wash away the nasty stuff and the right angle grinder with the 3M pad will take care of the gasket surface.
Timing plate goes on this side. Oh and don't forget to pop out the front and rear crank seals from the inside out of the covers before you place them back on with sealer! They come out with one tap this way. When you try and remove them from the outside (after assembly) they will take you a while longer, depending on your automotive tech skills =]
Cover plate goes on this end.
It's always a time saver to scrape away the old gasket sealer away with a sharp scraper. Then follow up with the grinding pad and it will be super shiny just like from the factory.