does the half pound refer to the weight of the bunch before trimming, or the weight of what you have leftover after trimming?

It all depends on how the ingredient line is written. If the instructions include cleaning the ramps then the assumption is that the weight is for the unprepped bunch. If the ingredient line reads "8 ounces trimmed ramps" then I'd buy 2 bunches and back into the weight. As Petitbleu noted, consider the dirt on the bulbs too!

Looks like the recipe is calling for 1/2 pound ramps before trimming. I don't know how the ramps that you buy are packaged, but the ones we get here are often sold or kept with big clumps of dirt around the bulbs. If your ramps have a lot of dirt on them, I would clean that off before weighing them.