1965 Mustang Full Quarter Replacement Advice

Do it the way Ford did ,under the roof .
Get a spot weld cutter and drill the spot welds out .The lead must be removed first but keep heat to a minimum so you do not warp the panels .The quarter slips up under the roof because the roof was installed after the quarters .There will be no stress on the panels .You will have to start by removing the back glass ,the headliner back at the quarters ,and it is best to remove the carpet so you do not start a fire .I always remove the gas tank when welding around the rear of the car . The new quarter slips up under the roof and it is not easy sometimes to get it under but it will go .You will find it is much easier to do it by slipping it under the roof as it is supposed to be .Cutting the quarter below the lead line means a long weld that has to be made and if to much heat is applied it will cause warping ,not to mention the extra body work . It will be a lot simpler and cleaner doing the way it was from the factory .