Like others have said, I would put them on any thing above a stock 6 cyl. .. I have twisted a B body pretty bad, had to jack the low corner up to get the door to close right , before welding in a puny 4 point bar, it helped tremendously, but wasn`t enough to completely cure it.
If , u drive around w/ a stock 440 and don't push it , u can probly get by w/o it.
A 2 door post is a little stouter than a hardtop anyway. Me, I`d subframe it anyway ! Level ur jackstands if doing it on the floor , especially if ur doors open and close right when leveled.----------JMO
