It might be awkward (and im kind of guessing) but it might be handy to compare the frequency curve against some usual choices. Apart from the sensitivity and frequency range etc of the speaker which might look the same as other guitar speakers, there could be a substantial variation in frequency response I guess, though I don't know what would effect that? dust cap size? cone material? voice coil construction? Interesting idea though. i hope it works out. thats just my feelings on it.
The material of the cone will have a large effect on the sound of the speaker-- too flexible, and it becomes undefined in the lower freqs... too stiff, and you'll get ringing at higher frequencies! A paper pulp seems to be a pretty good compromise for the cost-- obviously you can get speakers made with kevlar, hemp, aluminum etc. and they will all have different rigidity.
The voice coil will have an effect too-- it can be over or underhung (the amount the voice coil protrudes outside of the magnet). If I remember correctly, overhung will give you better bass response, but will affect the highs. The opposite is true also.
Many different ways to change the speaker, but only 1 person can say whether it sounds good to them or not :)
