I don't know of any book that is exclusively about performance. But there are bits here and there. Try the back issues of www.virtualindian.org
there are severall articals on performance. Jerry's new Scout book has some info on the old factory racers.
WR wheels get 52 cid. 74 Chief wheels get 57 cid. 80 Chief wheels get 61 cid.and very short engine life. The WR wheels with WR rods are a very good choice for a sporty solo bike they change rpm. easily and feel right. The 74 Chief wheels with after market rods are the best choice foe 2 up or a side car. More luging power, they feel like a light Chief.
By all means use pistons that pop up about the same amount that the Bonney pistons did. This opens the "corner" into the cylinder nicely.
Check out my latest project http://groups.yahoo.com/group/VirtualIndian/files/mule1.jpg http://groups.yahoo.com/group/VirtualIndian/files/mule2.jpg
I don't know of anyone that is reproing the Sport Scout frame castings so you will have to re tube origional frame or build a completely welded up frame. Check out the back issues of the Virtual Indian in the blueprint section the 640 rear section is drawn and the center section will be up early next year.There is also a doit your self frame by Frank that could be used for either the Scout or Chief engine. If you decide to do somthing with light frames let me know. Alot of the old racers tilted the engine forward (bottom front of crank case in same spot trans raised)to increase cornering clearance.