Lower block:


Harken 2629 BLK-57MM CARBO TRPL RAT.W/CAM ($221). You'll need to add an eyestrap above the cleat to serve as a becket.

Alternate lower block:


Harken 194 BLK-2.25 IN. LP TRPL HEX W/CAM ($161)

Upper Block:

Harken 2640 BLK-40MM CARBO TRIPLE ($82)

The combination of these blocks gives you the lightest weight (19.5 oz) and lowest stack height of any blocks on the market.

The worlds boats in Mexico had Harken 194's and the 2640 40mm Carbo blocks on the boom. I like the Carbo Ratchamatics because they're lighter (all of 3 oz) and the self-releasing ratchet mechanism lets the mainsheet pay out much more easily, especially in tacks and in light air.