That power supply wont work properly by itself. It is only constant voltage, not constant current, you would still need to and a driving circuit, 40V is high, what leds are you using, also what cuntry are you in, the minimum AC input voltage on that PSU is 176V, wont work in the USA.
I would not buy into plastic heat sinks, you are not the one benefiting, the manufacturer is. I cant really visualize your cooling system, heatsinks can be bought very very cheap,say $10-$15 if you know where to look.