I have seen (a lot of) PSUs with the cooling fins directly in contact with the casing. In one case the case was even tightened to the fin with a screw.
That is why there is rubber (or something like it) for insulation beetween the mosfets and the fins. And that is why I always ground the fins properly when modding PSUs like this.
And about the choke. Has anyone seen those chokes in older power supplies? no. For exmple I have not seen a single AT-psu with a choke. New more powerful psus have those chokes because they need to meet certain standards that they may not cause interference, "ripples" in the electrical network. The choke comes necessery when there is for exmple 20 computers in a single room, (schools, etc) as the ripples caused by all the switching psus would be enormous. Modding a single, or even two computers this way in a normal household causes no problems.
edit: I have modded PSUs like this before. In my own computer the modde psu has now lasted about 2 years without a problem. Thinking about computer hardwares life cycle, I do not require my Psus to last for ten years