Hi,
I had a look around on the internet, and i found this:
**broken link removed**
I will attach the circuit shown from this.
It is not identical, but it is so strikingly similar that
its clear to me this arrangement is a working design.
As Mr Partridge has said, it looks like the caps are correct
as drawn (sorry about that), although it seems there was
some confusion about that from this source too.
Positive to the base, in each case.
The author of this piece also goes on to say that the caps
have to be tantalum, but doesn't really say why, other than
standard electrolytics aren't up to it and may explode or
fail. My guess is that the ripple rating needs to be quite
high.
I still don't really see why diodes are included across the
windings, but there it is.
JBatt,
as your inverter is still not working, i would suggest you
check carefully the direction of each 12v winding.
It seems this circuit is a practical working design, and i
can only think that your windings may not be correctly
direction-ed.
Other than that, theres component failure, or a wiring fault.
There aren't that many parts to check, as Mr Partridge says.
Best of luck with it, John