on re-assembly, having the front open slightly so that I could put some pressure on the other side of the trackpad behind the holes for the screws made it easier to reseat them
if you open the front case slightly at this point a little pressure on the trackpad helps to lift it - but just a millimetre or two.
the trickiest step on re-assembly is reinserting this back-folded cable into the socket and then making sure the retaining flap (now hidden) is firmly down again. You can tell if it is still up (and so the cable loose) if the cable does not feel flat when you run your finger lightly over it.
This is easy if you use the small lugholes on the left and right sides near the top edge (which cover philips screws) to insert a spudger or fine slotted screwdriver and then work along the top with another spudger as if you were using tyre levers on a bicycle tyre. when you get to the middle, repeat from the other side.
these 'green' tapes are orange in my mbp