[Diabolical Artificer]

"TO5 sized transistor heatsinks." was going to suggest that too as Martin did but "Those slots would have been expensive to cut in an aluminium heatsink, and not necessary." as David says, same goes for the threaded inserts and look at the size, way too big for TO5.

Also being made out of ali & not a ferrite type material EG a conductor without a insulated covering rules out coil formers surely.

Andy.