I recently purchased both a Carrera 73653 and an Autavia 73663. With them being two totally different models, i'm surprised that the reference numbers are so similar. That said, They have the same movement, same shape case and the same dial layout.
Hi Matthew, congratulations-both very nice Heuers! For clarity-the model numbers follow a standard Heuer format at the time across the manual ranges and are broken down as 736=Valjoux 7736 5=Carrera 6=Autavia 3=stainless steel case so you can hopefully see why the numbers are so similar. Many thanks, Steve