I have built up the terminators from the second starter set now; just a few cut-and-shut changes this time. One of the stormbolter/fist guys was given a heavy flamer from the spares box; the other had both arms replaced with lightning claws. One of those stormbolters was transplanted onto the assault cannon body - see the pictures below.
The sergeant and the chainfist figure were left pretty much alone, apart from the wings on the sergeant; easy to remove, and it makes the two figures look slightly different.
Finally, I raided the bits box and put together two more terminators using the left-over arms; one of the bodies is a 'real' terminator, the other one was from Black Reach. I will have to add a bit of iconography with green stuff to blend them in, but the ornate arms help to get it started. I have given the cannon guy a greensuff hood already; more to come.