I have never owned a Greener so can't speak for the "Original" but on other makes I have owned which used a crossbolt they did not appear tapered, though I never actually measured one of them.
In the D M Lefever catalog on his New Lefever which used a crossbolt he did state hs bolt was tapered. He also used a stop screw on the right side to prevent the bolt from sticking.
When used in conjunction with an underbolt the crossbolt's primary purpose it to resist the springing of the frame.
In the case of the New Lefever only the crossbolt was used so it served the dual purpose of both holing the barrels shut & resisting frame springing.
