Ok, I've now finished re-doing the heatsink (and the whole computer as consequence) for the fifth time, and I believe I've had enough. I'll be buying a new socket 1156 HSF in the near future.
GTVic's idea is great but unfortunately it's not likely to apply to every motherboard. I went to the hardware store and got some bolts, nuts, and washers. Every time that I assembled the whole thing, CPU temps would be very high. After unseating and reseating the HSF, from looking at the thermal paste, I always saw that it wasn't making proper contact on the dead center of the CPU. More fiddling ensued (4x over), unseating, reseating, moving, tighetning, loosening, etc, I added springs to the bolts, until I realized the actual problem: the metal piece that attaches to the bottom of the Ninja is only wide enough for S775, and the (former) push-pin holes just barely make it over the 1156 holes.
What happens is that said piece also makes contact with the CPU socket retention frame (since it's smaller than it should be), which in turn creates "lever points", so to say, on the socket's edges. Which leads to the heatsink never really being properly fitted because the applied force is uneven. Also, because of the motherboard holes not being dead center with the Ninja frame, eventually as things get tightened up the bolts will start to go on an angle, thus wasting even more pressure.
So right now, with an i5 760 at stock settings, I'm doing 65-70ºC under load (down from 85 earlier...), which is definitely very subpar. I'm tired of removing/putting the board into the case, so it's going to stay as it is for now, until I get a new HSF.
GTVic: many thanks for the idea anyway
