After over 3 days of failed attempts I have finally constucted something which works fairly well. The 2 individual mechanisms were quite simple; an eccentric cam to create the up and down movement for the body (which also lifted the 6 main legs) and a rocking mechanism for the two tapping front legs.
The BIG problem was linking the two together so they worked from one handle and at the correct speed. I tried various methods to avoid using cogs because I just didn't feel confident I could make them well enough. It was fairly obvious that this was the only solution though. After about 4 sets of cogs I finally got a pair that worked smoothly.
The finished product looks crude but does work better than I could have hoped.