I assume you meant Maxi crankset, Spirt front derailleur and Ambrosio rear rim. Everything points to an early SHB model. In 1974 the Sekines definitely had the brand on the downtube and Shimano components as I worked in an LBS that carried Sekine starting that year. Pretty sure it was also that way in 1973, but it could have been a running change in 1973. I'd say pre-1973, but 1973 is a possibility. The rear rim/wheel is almost certainly a replacement. The date would also indicate that is of Japanese origin,as opposed to Canadian.
The SHB model was second from bottom in the lightweight line-up and was a very popular bicycle for good reason. While the frame was somewhat heavier and less resilient than comparable European bicycles, it was much studier and took a lot of punishment. They were the perfect choice for a teenager's first 10 speed. They were also a very good value, having better components than the competition on the price range. The component selection and assembly was excellent. Wheels were always true and nicely tensioned. The paint was beautiful, with a a very deep, wet appearance (except for an ugly olive green they had). In general, their quality control was beyond reproach, and to this day I rank them second only to Miyata in terms of mass produced Japanes bicycles. Competition was the Raleigh Grand Prix, Peugot U08 and Gitane Gran Sport. We sold all these models and the Sekine SHB outsold the combination of all three models.