I realize that the chassis and the plate don't have the same number !


they're not supposed to. the Trim Tag has the Fisher body number, which doesn't really have anything to do with the Buick sequential production number.



can i put the "gran sport" on my Riviera After the restoration ?


you can put anything you want on it, it's your car.

it would be pretty shady to try to sell it to someone as an original GS, though. just tell them it's a replica Gran Sport and you'll be fine.



This car comes from a car break to have so many different origins.

we call it a "junk yard" or "scrap yard".



Where can i find the dimensions of my frame ?


there's a guy claiming to sell them on Ebay.
http://www.ebay.com/itm/1965-Buick-R...-/321114962657

we don't have a chassis manual which would cover your car ( 1960 and 1966, while your chassis version existed from 1963-65 ), but you could buy one of those.

rivowners.org may have something.