Ideally the heat-sinks should cover all the chip's surface, so you could trim a couple up or maybe use a thin copper sheet as a heat spreader and sink both the main chips together with 4 or 6 of those
heat-sinks on top.
You'll need at least some air-flow >n64, but you can tell the heat-sinking needed because you can easily measure the power going in, so you know how much heat needs to be dissipated.
For example; I measured the DC, and it needs ~2400mA on it's 3.3V line, this is to power the CPU and the PowerVR, so thats about 8W between both chips, a
quick google says the CPU ~1.5W so the PowerVR ~6.5W . You need the temp rise to stay under ~25°C, for the CPU this means a hs better than (25/1.5) ~ 16°C/W, for the PowerVR (25/6.5) ~ 3.8°/W. So the CPU would be more than happy with one of those ebay sinks on it, and the GPU would be fine too if it had a fan nearby.
Similarly for the GC, IIRC it takes ~6000mA on it's 1.9V line to power the main two chips, so there's ~12W to get rid of between them. You could put four of those sinks covering both chips and it would be more than adequate with a fan in the system.
Again, these are only estimates but they're pretty conservative, and they do prove that you don't need too much cooling to keep these older systems happy, I'd say pretty much any >10mm high heat-sink should be fine, just try it out.
