They told me to buy the hardened pushrods with my edelbrock rpm performer heads so i would say you will allso.I am shore some one on here can tell you forshore.
Stock GT40P heads use pedestal mount rockers, and therefore do not need hardened pushrods. If you upgrade the heads to use stud mount rockers, then you would need the hardened pushrods.
In either case, you ought to consider measuring for correct length to make sure your valvetrain geometry is ideal.
Still measure them. FTI custom grinds use the standard base circle, so stock length (6.272) should work fine, but it's always nice to be sure. Kinda like how you are going to degree the cam, because that's the Right Thing To Do(tm).
Very likely right in the neighborhood of the stock ones. I ended up with 6.300 myself. It can vary based on the head, valves, and rockers. You can get a good pushrod length checker from Summit for about $20.