ECP's are available at the EVGA Store here:
link Full compatibility list at the bottom of the post.
I'd kind of planned to clean up my photos of measurements for the ECP, but didn't get around to it. Oh well. Regardless, people still ask for the measurements of this panel, so I figured I'd put up a sticky for it. I apologize if someone's made a similar thread, so if you have, please PM me and I'll gladly include a link to it here.
All measurements taken with a digital caliper by yours truly. Measurements are in fractions, because those were more accurate and scaled better than cm or inches.
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Here's what I did with mine, eventually. I basically used a blank 5 1/2" cover panel as the template. I then used a dremel to cut out a square just a little less area than where the holes are. I found the bottom area, where the main connector plugs in is the toughest area to get right, but you'll have enough wiggle room at the bottom if you were careful on the initial cut. I ultimately had to file the bracket (not ECP) down until I was able to fit in that bottom connector. After, just use some screws less than a 1/8" diameter with a nut to tie down the ECP (washers optional).
Using a Mountain Mods anodized black 5 1/2" bracket:
link link 
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And the finalized 5 1/2" bay:
link 
I have 3 of the ECPs, and I can tell you that each of them had a slightly different measurement in terms of where the mounting holes are centered on the whole PCB (within 1/32"). However, if you follow the template, mark your holes carefully with
your ECP, make the holes slightly wider, you should have no problem. The PCB is flexible, so be prepared for that to potentially throw off very fine measurements.
Motherboard compatibility list:
W5520: SR-2
X58: E759, E760*, E761, E769*, E762, E770*
P55: E657, E658, E659
* denotes that ECP does not come with the board and must be purchased separately