I finally got it working and aligned. And I've just had my first QSO with it. Conditions seem to be pretty bad but I got a 599 from Belgium.
So my problems were:
1. Enamel not fully burned off on one of the connections to T1, despite holding the iron on for at least 10s.
2. Not aligning with a dummy load connected. The instructions (as far as I can see) only say not to have an antenna connected.
3. The LPF capacitors. There seems to be a common problem with C25 and C26 in the 20m and 30m kits. As I didn't have any 560pF NP0 capacitors I've actually used the more recent W3NQN design as documented in many GQRP club publications and on their website. I left C27 and C28 on the board as their 290pF is almost right (the design needs 296pF or in practice 2x150pF) but L1-L3 need slightly different turns and C25 and C26 become 470pF. There is also a 68pF cap across L2. I now get 4W with 15V, so some more tweaking may be necessary.
I set the frequency by listening to the 27MHz clock on my FT450D. I've also confirmed with the Russian time station RWM on 9996kHz.