Proper board layout for high power SMT FETs
It is annoying when all the information isn't in one datasheet, but you can typically find a lot more info on the manufacturers website. In this case, everything is on here. Specifically, read this. Basically, thick copper and thermal vias are what you need. Exactly how much extra copper you need to deal with the heat will depend on your application. 

If you want to dissapate the maximum 325W, you're going to need some serious active cooling, with heat pipes and fans. You can see that a normal PCB will not be enough for that scenario, because the thermal resistance with 6cm^2 of single layer PCB is 40K/W, more than 2 orders of magnitude too high. The max thermal resistance of the case itself is 0.4 K/W, so it would be dodgy running it at 325W even with amazing cooling.

I would guess that to get rid of 100W of heat, with the typical 0.2K/W case resistance, you would need a solution with a resistance of less than 0.3K/W, which is a pretty amazing heat pipe. 

Edit: to answer part of your question, yes an aluminium IMS will be needed at the very least.