Converting to a salt and filtering will purify it some. If you can get the freebase to a cream or light khaki color, then convert to salt and filter, the purity should be at least in the 90s. If you're looking for purity, don't use lemon juice but citric acid. Many acids would be appropriate, but keep in mind that there are ones like acetic (vinegar) and HCl that are much easier to work with, because unreacted acid will evaporate.

I can't speak too much on harmala extraction as I haven't done one YET.