AOA
Zulfiqar sb probably i could not explain you properly at earlier,as u definitely knew that actual length and width of RR are bigger to the sizes of donner car of Mercedes 115, therefore we reduced the length n width sizes of RR up to the actual length and width of Mercedes (in proportional manner) so the actual chassis, engine, engine room ,front / rear suspension, floor, all door bracket, front pillars, roof , lower part of trunk etc etc of Mercedes could be used,there left just one difference of some inches in wheel base (in length wise not in width wise) which we meet by adding / welding a require piece in floor
(i am sorry for the inconvenience i never been at any public forum more over my language as well technical knowledge is not good as people at here )
thank you