I received the parts I ordered for the Prime yesterday, and started work on work on him today.
I cut down the hive tyrant legs (reducing the size of the ankles and shortening the thighs) and scratch-built a bug-like abdomen to match those of the other beasties I've converted. the abdomen still needs the addition of armour-plates on the top and work done to the tail tip.
I'm looking forward to starting work on the thorax - I'm imagining a larger bulkier version of a warrior, with the head nested inside a hollow surrounded by plates. We'll see how that works out!
also, to anyone interested in the abdomen's basis, it's just made from 7 layers of plasticard (not sure if its 1.5 or 2mm) roughly carved into shape: