If you go with the double blocks, you can then later add a pair of singles by the grommet and cascade to 16 to 1. You just need a second line (on each side) tied off to the double, up through the single, and cleated off to the clam cleat on each side of the mast. A possible problem with the quad would be if there weren't enough room above the boom for it, in other words, it would run into the boom when really cranking on the downhaul. Doubles will bypass the boom, and avoid the potential problem.

Peter Shapiro
P19MX