[Brian Duff]

you don't want blocks.
use small dyneema line and it will remain slippery enough to move easily when retracted.

I strongly recommend making them adjustable from above, as opposed to along the boom, so that you can adjust them even with the mainsail down.

I like to have my lazy jacks stowed when the main is down , so that its easy to hoist and clear to sail, then just before dropping we set them, drop the main, furl it, then put them away.

Ideally the fall of the lazy jacks from above is run internal on the rig.

That said, my current boat at 32' is too small for lazy jacks. (IMHO)