Registering a sled

My kids are getting to the age and size that they "need" their own sleds. I have been able to find some of the old Yamaha Phazers in Pennsylvania for good prices with low miles but they are all lacking paperwork. I'd like to get them registered solely in NY and can have my ex who is a NY resident do it (I am a PA resident) but am not sure what all it is going to take and how much hassle the lack of paperwork is going to be. She will help but I need to make it go smooth.

I took a chance and purchased one and recieved a bill of sale and the original, but unsigned by the dealer, Manufacturer's Certificate of Origin. I have a line on another but it was last registered in MD and he doesn't have the papework either.

Any advice?

TIA