Can't tell from the picture but those are not "bolted" to the metal plate. Typically TO-220 style are "bolted" to a heatsink with a non-conductive silicon paste between the device and heatsink. They can get hot so "hot gluing" them down would not be recommended. Take a look at this for typical mounting.
I haven't seen a mica plate in ages but some heatsink kits do now come with a silicone rubber pad to go between device and heatsink. You can either bend them down to mount on the existing plate or use an aluminum heatsink kit on them if there is space available for one. The devices are rated for up to 175 C so I would think they might get hot depending on power across them and duty cycle.