I found a few small pieces of glass/sand from the blasting (finish appearance ) process embedded between the fins of my .49...I picked 'em out and dis-assembled the rest of the engine (except for taking the crank out ) and cleaned it as I always do.

IMO, if there is a little bit of flashing at the very bottom of that particular port, you should be able to remove it easily, but I think that when you put the backplate back in, it will "mask" that area anyway, so that little bit of flashing is not going to make any difference as far as flow is concerned, whether you use side or rear exhaust...