Nate

Yes, I'm guessing the date wheel has been replaced - not sure what other ones are compatable but the standard HEUER Cal 11/12 is silver with black numerals. Also may be worth getting a watchmaker to have a look at the movement to see if other parts have been replaced / compromised as sourcing parts for these is sometimes less than easy. Depending where you are based, I am sure the OTD community can recommend Heuer specialists like for example Nic Green in the UK or Craig B in the US

There is a Cal 11 bridge on ebay Italy:

http://www.ebay.it/itm/Heuer-Cal-11-Bridge-Buren-Chronomatic-Autavia-Monaco-Carrera-Vintage-part-8500-/222592208354?hash=item33d3878de2:g:UjsAAOSwaEhZIDXN

I cannot locate a Cal 11 or 12 date wheel currently on ebay based upon a search - they do come up from time to time at circa €100 - worth posting a Want to Buy (WTB) on chronotrader.

The final result of a project is really fulfilling though and the search for parts is often part of the story

Good luck