Yeah, it'll prolly be better to get a card already with the L2 Pro. Problem is other heatsinks like AC S1 or S2, Scythe Setsugen (not to mention Musashi) will be simply too big and overhang the card.
Perhaps it would be a good idea to look for a 5670 (or similar) with custom PCB, where the GPU is shifted towards the I/O bracket. A card like that, fitted with L2 Pro should fit your bill. The pic shows what I mean by "shifted GPU":
Or you could try this one (provided the pipes will not interfere):
More pics of this one - click
Another fanless 5670 - but this one will prolly be too long :/
One more card seems to have the L2 Pro:
Speaking of noise of the L2 Pro - it's not a champ, true, but can be easily made almost silent by either downvolting the fan by means of a, say, Fanmate, or you could play a little with Rivatuner or even with the bios. Radeon Bios Editor tool is v easy to use and will sure tame the fan.