I can't see that anywhere. The 387s only operated on Thameslink for a few years as a stopgap measure to allow the 319s and 377s to be withdrawn quicker than when the 700s arrived. After that, they've ended up in the GTR lucky dip of Electrostars, which is sort of what was intended for them in the first place.
There is a thread about this
here and additional posts
here,
here and
here. Some of them even suggest that the reason for the pantographs was because they were intended to be used on HS1, which is...interesting, to say the least.
Does anyone know if the pantographs are still there, and if so, whether SE bother maintaining them anymore, considering they never run under the wires?