Coincidentally a package from Amazon UK containing both of those books dropped through my letterbox today - they were the two obvious choices that came up when i went looking too. I've a Hammer F3 arriving next week, and have never used a spindle moulder.....
A quick look suggests that while they cover quite similar territory the Stephenson book (possibly the British author you are thinking of OPJ) is quite a lot more detailed, and covers the technical issues in considerable depth. It looks like a bit of a mine of hard and detailed information. The focus is European with a Felder and professional/industry machine flavour, and it was published/updated in 2007.
The HSE seem to have had an input too with recent safety legislation in mind - it's likely that his set-ups etc. should comply.
The Lonnie Bird book is less detailed but more descriptive, was written about ten years ago and is as already said very much in the US idiom - lots of cutter heads with brazed inserts and so on, and based around the typical US DIY/lower end professional 'spindle in a square cast iron table' machines.
There's probably more on safety and general considerations to bear in mind when operating the machine in the Bird book (in the US context at least), but that's only a first impression.
Both look very much worth having, although there's probably a fair bit of overlap...
