The scratches... it's hard to tell from a picture. The little dots in the bearing? That's flak.
If it's at all possible, write it off as a learning experience, buy another gasket set, and yank the engine back out.
Some motor oils are waxy and leave buildups here and there that the hot tank won't remove. Along the top side of the pan rail and over the rear cam bearing are good spots for dust and shavings to get embedded in the wax, where they then depart when the motor is fired up.
You need to check the insides of the wrist pins, and behind the rings. The timing chain can sometimes have a bunch of crud in it; wash it in gasoline or solvent and soak it in oil before reinstallation. Use a rifle cleaning kit and run brushes through all the oil galleries in the block and crank. Take the heads to the car wash and use soapy water to blast out any flak in the valve springs. Make sure you pull the oil filter adapter and clean behind it. Clean *everything*. And if you're using the stock intake, pull the sheet metal cover on the bottom and remove the pound or so of carbon and dirt behind the heat shield. Make sure there's nothing hiding behind the oil pan baffles.
Some shops use shot blasters for cleaning parts. The tiny steel beads can get trapped in odd places, to break free later. I've seen the steel shot fall out of a cylinder head's water jacket into the bores when someone was setting the head down on the block..
You'll always have some sparklies from a new motor. They generally come from the timing chain and the valve spings. Back when I was in the business, I specified an oil change after a 20-minute run in, then again at a hundred miles. Cheap non-detergent oil is perfectly fine for that. One of the fancy neodymium "computer magnets" in the pan, and one near each drainback hole in the cylinder head will help catch stuff if you have an engine failure. Remember, the small block Chevy has a bypass filtration system; only about half the oil makes it through the filter in normal operation. The Chevy's oil pump is a gear type and will happily pass sizeable chunks of debris back around and around and around...
