Do you want to know how to register while you are outside of New York state?
no
Do you want to know when you will receive your registration documents?
yes
You should allow 6 weeks for your registration documents to arrive by mail, and allow 90 days for your title certificate to arrive
and it doesn't matter if the registration address is different than the address where I want them sent?
You must include a separate note with your Vehicle Registration/Title Application and clearly print the alternate address.  Do not write the alternate address on your application.
Did you write the alternate address on your application?
whoops, yes
DMV will print the alternate address on your application
Is there more I can look at on the topic?
Yes, I can link you to more Registration information
what do you accept as proof of ownership for a 68 Mustang?