The Shimano Eagle II and Thunderbird II derailleurs were introduced for the 1977 model year, so there's a good probability that the 05-77 is a date code, in which case the bicycle would be a 1977 or 1978 model. The bulge formed head tube is the same as that used by Sekine, though I don't recall a Sekine model with stays that were crimped onto stamped dropouts. Still, the head tube suggests that this is an Asian (and probably Japanese) manufactured frame. Consequently, the number stamped onto the head tube is likely the model number for the client and there may be an actual serial number elsewhere on the frame. I concur that the frame is bent and that the bicycle is department store level.

Edit: The number format on the head tube reminds me of that used by Sears on their bicycles. It could be a Free Spirit model or similar.