Well , hesitant to reply, but i think every one would agree with me and say you would be better to replace the whole quarter panel , unless you are one hell of a welder and body man with year's of experience. My brother in law had his body man try that exact thing on a 1963 that you want to do ,and even in primer you could see it was not straight. They used two half panel's at that time you could not find full quarter panel's. This car was broad sided in the right quarter and totaled. They ended up finding a car that was hit in front very hard early in time and was rust free{very lucky to find} and put their front clip ,cut at windshield post's and floor area at seam in front floor area.This was a factory 63 SS 409 car ,but went from a palomar original color to black and you could not tell this was done.Don't mean to discourage you ,but in the long run you will have better result's in the end.