DX derailleur 1990 maximum teeth?
A quick detour into BING produces the manual from this link:
RD-M650
and partially shown below:


For your derailleur you're correct, 32T is the biggest cog you could have at the rear. It's possible a freewheel with a bigger cog (34T) would work, but you may have to block off that cog by adjusting the limit screws if the derailleur cannot handle it.

I don't recall these derailleurs being available in different cage lengths, they were long cage by default.