Hi,
The later painted tanks on the 175/200 were the identical to the previous chrome 175 tanks. Bridgestone were simply trying to modernise the look of the bike without spending major money (and, presumably they saved the cost of chrome plating the tank).
So the tanks are interchangeable, as long as you use a tank from a late model 175 that had the oil tank mounted n the side of the frame. The very early 175s had the oil tank mounted underneath the fuel tank and the oil filler neck sprouted out just behind the steering head. These early 175 tanks have a huge cut-out at the front to fit round the steering head an oil filler, and the should be fairly obvious on examination.
Hope that helps,
Graham