No, "adding" up several different kinds won't give you the same effect. Lighter crystals are sweet and carmelly, and the darker ones are raisiny and almost like burnt toffee.
I keep crystal 120L on hand, but I've never used anything darker. 120L is easy to find, so you could probably use that if you can't find the grains called for in the recipe. I think Midwest supplies has the darker stuff, though, if you want to get the exact ingredients. The darker one that's in the recipe will have more of a burnt sugar taste to it.
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