With EXP core 2,0 only one friction plate is removed and exp ring and center clutch installed. I think that you have to remove att least three friction plates and steel plates if you just add exp. That leaves guite much power to small amount of friction plates. I don't think that those plates or exp's friction section would last long... So not cheap in the long run...
Just my thoughts... I wouldn't try it... Gas Gas EXP = Honda 450 EXP