A quick update: Today I reached the end of Act II - on page 72. It's currently at a 'Draft 1.5' stage, as I made a few ad hoc tweaks along the way as-and-when they popped into my head or I stumbled upon something in my notes I had forgotten about.
Next up I shall go through all of Act II and make some changes. It's also a good way to get several days worth of writing straightened out in your head within a much more compressed time frame in advance of starting work on the following act.
I'm happy to say that it's coming together nicely!