You can usually get them on Ebay in 13/16ths or 7/8ths. If you can't find the size you need, then contact some of the sellers, they might be able to help. I'd find out what size master cylinder the 280zx uses, then buy one of that size to suit the 280zx. As the 280zx usually run rear discs, the rear brakes shouldn't drag like it would if you used a rear drum master cylinder.