They should all work. The space around the socket is standardized so this doesnt happen. I've seen the zero clearance you're talking about, however. Typically you can mount the block and push 'away' from the ram and tighten down (1-2mm is all it takes) so it doesn't push on it. There's some play on the mounting.
If you're concerned, look up the dimensions of that ek aio block and look at the dimensions of some aios your looking at. Obviously anything smaller won't run into that rare (and typically 'fixable') occurrence.