Yes, the "L" is there for "Lumenized". Date code is "RM" or 1953. The front rim has threads, but I suppose you could use slip-on filters also if it's big enough to go around the edge. I don't know how big the lens caps would have to be offhand, but I can measure it tomorrow. For tonight, I'm cramming for tomorrow's exam. NICET knows no mercy.
Per request in PM, this is sold, pending payment.