Agmetal- You will learn that indexed system are FAR more dependent on a number of factors that weren't too important back in the day. Besides the obvious family of compatibility of cog count/lever detent count and brand family there are other factors at play. Inner cable diameter, casing grade, casing end caps, rear der pulley design, chain and cog tooth profiles are only some of the more important ones. back in the late 1980s and early 1990s there was still less then complete understanding of these factors and also a lot of pre index product in the manufactures' pipe lines. As the product slowly got used up these factors have been less variable, until a used bike is dealt with... Then a consumer's motivations to use what's at hand comes into play.

What would I do in your case? first confirm that the families of compatibility are right. Right number of cogs and lever detents. Proper SIS inner and casing (and the casing in the photo looks spiral wound, not SIS). Base line the limit screws without levers controlling movements (pull exposed cables to move the ders). make sure the lever has over shift and re centering movement without hindrance. This, to a good mechanic, would tell a lot without much experience. Andy.