I too would recommend Modular LED. I like what he's done by using the boards and eliminating the need for soldering your led's together. I was thinking of building a fixture but will have to wait because my tank hasn't yet been delivered.
I was originally going to use the AI mounting rails.
http://www.modularled.ca/ai-sol-mounting-rails/
However I was recently at Rona and they had different lengths of Aluminum that were "L" shaped that would have worked perfect for mounting the heatsinks. The finish on the aluminum strips are quite nice and would match the heatsinks perfectly. It would almost look like they were made for each other and wouldn't look something like a frankenbuild. The heatsinks would be exposed but wouldn't look much different than how the AI SOL's mounted. Just a thought you might want to consider.