I had an Olympic purchased in 1978 that was exactly like yours with plain gauge 531, Sugino Maxy cranks, and Shimano Titlist derailleurs. Olympic was on a vinyl sticker on the chainstay which could have been lost on your frame. It cost $250 in 1978.

Nigel Land on the Classic Rendezvous list copied these specifications from a 1974 catalogue:
"Model 78/79 Olympic 531 plain gauge, cotterless chainset 5/10 speed.
Bottom of the range at £98.50"

Bottom of the range sounds harsh but this model equates to the middle range of competitor's bike lines.

I recently purchased a Falcon Super Route which seems to be identical to the Olympic from nearly the same time period (1974-1978). It's sitting behind me in my cube as it's my daily commuter. It has long point lugs and a normal flat crown and chrome only on the fork. I'd take a picture of it but I have no garage door which is de rigour. I paid a lot more than you did for it but it was still a great deal.