My car weighs 3650 with me in it. To me a "unopened" stock engine is stock heads unported, stock rotating assembly, stock cam and valvetrain that's not had the heads off. Since blowing a head gasket is not uncommon I don't consider replaceing a head gasket changing it from stock. Changing the timing chain or valve springs to me is not a factor in saying "stock" since they are wear items. I have only replaced the valve springs on my car. Anything that bolts on the outside of the block is OK to still say it's stock with boltons. That includes turbo, throttlebody mods, fuel regulator, exhaust, air filter, injectors and alky, etc.