To be honest, I think your not really making a lot of sense in terms of the build. If you really are purchasing 600 dollars worth of LEDs it would, IMHO- be a major mistake to even think about the items your contemplating.
3 good reasons.
(1)
You new shiny LED's presumably are start mounted - Thus they REQUIRE a perfectly (I.E. CNC machined would be nice) surface to mount to, ANY air/debris in the interface between the LED star base and the heat sink will severely limit your ability to suck heat away from the actual LED die which is mounted to the star.
Those items have not a flat surface in sight.
(2)
Those items appear to have plastic all over the place, inside, outside etc. Plastic is a very nice insulator...
(3)
I have something like 28 LEDs mounted to a 11x7 heat sink with CNC machined Fins that have grooves in them, I have them mounted in a canopy that is completely exposed to air beneath the lights (i.e. is suspended over the top of the tank with a very large space between the tank and the canopy). Even running at 40% power I was getting too HOT. I installed two variable speed fans and drilled a bunch of holes in the top of the canopy to promote breathing and now am FINE... but thats with almost 100 bucks in heat sinks (they are even black anodized to increase radiant heat transfer) and another 50 in fans.
(4)- bonus reason-
You will be replacing 600 worth of LEDs if you don't pay careful attention to their temperature.
It is NOT worth playing around with heat sinks. I know that LOTS of people have them mounted to aluminum channel and they seem fine but everyone is using fans so far as I can tell and they are using a dispersed array design with the LEDs distributed over the entire tank so there is a good bit of space between them... if you go that route or similar for heat sink remember this fact when mounting your stars and you should be OK but get FANS.
The U channel at least that provides a suitable mounting surface- again- seriously advise against items you show in pictures... they look like door jambs.
One other thing to think of. Part of my cooling issue is that my design has the LEDS clustered as CLOSE as I could mount them into "spot light" or PAR groups, without the stars quite touching. Each group is about 14 LEDs in less than 10 sq inches of space on the heat sink. Most general guide lines call for between 2-3 sq inches of heat sink per LED and thats in a dispersed array with a standard aluminum heat sink with the fins etc...
so my build is fairly a-typical and this is causing me MUCH more heat dissipation issues than a dispersed array would pose... so remember this when thinking about my comments/experience/opinion, I am probably more concerned with this than others have experienced given the power density I have.