1969 Barracuda 340 Formula S Restoration

After a long delay, back at it again!! But first a question. Does anyone have a fix for a rear trunklid that won't stay up on a fastback?? I've got mine adjusted as much as it will go ( I think). Seems like the coil spring is weak.
IMG_3557_1280x960.JPGIMG_3558_1280x960.JPGIMG_3559_1280x960.JPG, but just barely stays open.