Didn't your 770 come with a scope and rings? If so why not just drop the Nikon in those mounts.
The 770 isn't the greatest of guns but will get you by if you don't mind it. And if it shoots decent then its great. I seriously looked at them but the more I read and the more I realize I wanted to do with my rifle the more I decided against them. Ended up with a 700 SPS Varmint in 308 instead.
But then I am not currently hunting with it, but making a long range shooter out of it. Not sure the Nikon you got but I do love my Nikon on my slug gun.
Anyway don't cheap out on mounts and optics if you can afford otherwise...I learned the hard way that things can happen and the extra few bucks could have saved me money in the long run.