they're pretty close, the floorpan will need strengthening, the doors will need to be replaced/modified, the rear will need strengthening etc..
i've done a speedster on a 68 (no folding roof) and up untill the the strengthening panels were there the car was solid (minimal flex over the saloon) but the next owner removed them and the car literally snapped in 2 around the door joints.
it's a risky conversion.