I've read that different length velocity stacks on triple carbs can change the power band. I'm thinking of using the Ramflo filters I have in a cupboard on my triple Delorotos. Do people usually have the velocity stacks under filters or just bolt on the filter and housing?

Put stacks under the filters. With that style of filter I don't think your length choices are going to be too varied. You're going to need a fairly short stack.