From your new figures the ratio between first and top is 2.586:1. The book figure is 2.6:1 for a Rapide so you have a Rapide first gear not the original Shadow one. If your speedo and rev counter were absolutely accurate then the revs in top with normal gearing would be 2,875. Your figure of 2,900 is well within the 10% error that many chronometric devices have so it seems likely that you also have a standard ratio on the rear chain.
Sean's first post states " Rear wheel is 19" and the larger 48T sprocket is in use. It also carries a 46T sprocket on the left side. " would this account for the slight difference?