for your space of 16 x 36 https://horticulturelightinggroup.com/collections/diy/products/260w-qb-led-kit would be a good fit 8 x 24.
or you could use the newer smaller boards in that space that do not require any heatsink
https://horticulturelightinggroup.com/collections/diy/products/hlg-65 2 or...