If the aluminium heat sink is getting hot, then that basically means that it's doing its job correctly and efficiently....the heat you feel is a good indication of this. Personally I'd be leaving it as is.
Jens hangs around EAB a lot, so you could post a question on there, or just e-mail him and ask him if you really want to know how it's attached.
You might want to mount a small fan at the side of the trapdoor (just to the right) to blow air across the ACA card and into the main part of the case. You can have an even larger fan if you mount it resting on the floppy connector and angle it down towards the trapdoor (you have to cut a tab on the interior of the 1200 upper case though for that). That's currently how I keep my Apollo 060 cool, and the case all at the same time (just the one fan).
