Can I Connect Two Totally Different Transformers in Series?
If you have two transformers, with their primaries in parallel, it's just fine to connect their secondaries in series. 

Their output voltages will add algebraically, which means if you have (for instance) a 35v and 40v secondary, you'll get either 75v or 5v, depending on the phasing of the two transformers.

You should limit the current that you draw to the capability of the lower current transformer.

If you have a large and a small transformer, you'll likely find that the small one delivers fewer volts per turn, so you'll need more turns for a similar output voltage.