Hi Cloggy,
There isn't much to be gained from the 55716. All the interest lies in the prefix number 087B. The 55716 appears to be more just an internal factory number. Perhaps they had made 55716 6E engines by then. I think if that number of engines had been made for the one buyer we'd know all about it as most Villiers sales were in penny packet numbers compared to todays manufacturing figures. We often forget how small the British motorcycle industry was when compared to today. Remember Honda make more bikes before morning tea than the likes of Dot, Cotton, Ambassador & Greeves, etc, made in a whole year.
I can't help much with Bond engine numbers one way or the other. Roy Bacon included early Bond motorcycles in his book but not Bond cars nor Bond scooters. I do have the engine prefix for the early Bond cars using the 125cc 9D engine in my own list but nothing else. Villiers engines got used in all sorts of devices. Recently a good number of them came on to the market here in Australia: all ex-New South Wales Railways. They were used to power gangers trolleys and finally the Railway decided to sell them off. With the prefix 514B they didn't get a mention in Bacons book either. It's not unusual to find an orphan Villiers like yours, hopefully someone will know.
Cheers,