A shorter piston does not change the the stroke or displacement. The same air compressed into an increasingly larger chamber only drops the compression. Decking the cylinders or heads would only bring you back to where you started. Unless you throw on a supercharger.
On the other hand, can you get a domed piston that will increase the compression and HP without dammage to the valves?
I have seen a few 88" bikes with cams and the high compression, BLOW the Socks OFF the 95" bikes with about the same mods.....88"ers got better Mileage to fuel ratios Also!.. It is IN the way they were PLANNED from the start to the finish... No hodge-podge tossed at them... Guess work better left to Others! signed....BUBBIE