While Tunturi is a Finnish brand, there is a good probability that it may have been contract manufactured in Japan. The frame features date it circa 1981-1984 when 600AX would have been OEM and Japan was the prime source for contract manufacture, due to low exchange rates. The serial number is the best indicator of whether it was manufactured in Japan, who the manufacturer was, and the exact year.

Given, the shift lever boss, there is a very good probability that it was originally equipped with 600AX. I don't now much about Tunturi bicycles but they were distributed in the USA, as there used to be small advertisements for Tunturi in the back of Bicycling magazine. 600AX is the successor to the 600EX, so there is a good probability that it may be a newer version of the 600EX equipped Professional in the previous post.

While 600AX equipped bicycles often came with aero tubing, this was far from the rule. Sometimes, manufacturers would make cost concessions to hit a certain price point and/or have a cost advantage over the competition. The non-aero tubeset, post, stem, handlebars and headset may well fall into this category and could be OEM.

The other thing that I would suggest you do is remove the seat post and check for the diameter, which is typically stamped on it, somewhere below the insertion mark. This will correlate to the grade of the tubeset. If you wan to investigate further, you can remove the fork. If Japanese, the outside of the steerer tube should be marked with the tubing manufacturer and a date code.