I've recently been pointed towards this Wikipedia article which lists actors considered for the part of the Doctor. I wonder whether there's mileage in using this to construct an alternate timeline of incarnations for the Doctor using this list. So, for example:
First Doctor: Geoffrey Bayldon Second Doctor: Valentine Dyall Third Doctor: Ron Moody Fourth Doctor: Bernard Cribbins Fifth Doctor: Richard Griffiths Sixth Doctor: Wikipedia draws a blank here Seventh Doctor: Ken Campbell Eighth Doctor: John Sessions Ninth Doctor: Judi Dench Tenth Doctor: another blank Eleventh Doctor: another blank Twelfth Doctor: Ben Daniels
For the blanks, either pick a name listed against one of the other Doctors, or choose somebody who was rumoured at the time (Bill Nighy was a popular one for either the 10th or 11th Doctors).