Have a read through Section 8.2 of this:
http://sound.westhost.com/xfmr2.htm , you are looking at toroidal transformers, doughnut shaped, so you can be 99% certain that parallel operation is safe but it is well worth the time to quote:

The transformer manufacturer's specifications will indicate if parallel operation is permitted. If you are unsure, measure the voltages carefully, and avoid parallel connection if the voltages differ by more than a couple of hundred millivolts. There will always be a difference, and only the manufacturer's winding tolerances can predict what it will be. With toroidal transformers, the windings are often bifilar, meaning that the two windings are wound onto the transformer core simultaneously. The tolerance of such windings is normally very good, and should cause no problems.
Sections 8.1, 11.3 and 12.1 are also worth a quick once over.

This is a must read for anyone playing with mains: http://sound.westhost.com/articles/electrocution.htm

If you're bored then http://sound.westhost.com/xfmr.htm is also worth looking at. In fact bookmark the site for a rainy day, there's lots of info in the Articles part and a lot of good projects too. Rod Elliott, the site owner is knowledgeable and well respected, if you are ever uncertain about anything electrical then it's always worth a visit to see if Rod has any advice.