Your better to go with smaller heatsinks and attach them together with some brackets from Canadian Tire or somewhere. Its pretty expensive to ship a 72in or 48in heatsink. Although having said that if you still want one that long drop me a private message or something we have gotten our manufacturer to ship direct for heatsinks that size, or you could come to Red Deer and pick it up
. That way your only paying for shipping once.
Everyone seems to have a different formula for LEDs but my calculator comes out at 160 for a tank that size. That's for SPS. (LxWxH / 324).
With a setup that size its going to be cheaper to go with a larger driver that can drive 60-70 LEDs.
Martin