Be certain that you are out of options with body shims and panel adjustment. If the car has not been wrecked, everything should go together properly with adjustments and patience. If the car has been wrecked, take the time to make sure your angles from back to front corners in the engine bay are equal. Also make sure there are no obstructions from the inner fender that won't allow full fender adjustment.
You don't want to mess with the vertical line of the door or fender to make up for a bottom gap. Mess with the shims. Adding a shim at the mount point closest to the door gap will close that gap. But you will probably have to adjust other areas before you get the result you are looking for. If this is a driver only and the doors open and close properly and the gaps aren't that bad, leave it alone and enjoy the car. Triumphs weren't perfect from the factory.