Round 2 hasn't included more optional parts from the original issue, have they? There were some optional parts in the '80s issue (the one molded in orange that said 'GTX' on the box...a front air dam and Superbird rear wing, IIRC. The box art I've seen for the original '74 showed parts for a Baja racer version.
IIRC, my '80s issue has the Road Runner scripts and birdies molded on the body, but the reissue from around 2004 doesn't have them.
The '73-74 Road Runners and Chargers are the only original MPC Road Runners and Chargers of that era I don't have..I have the the original '71 GTX kit (some of my favorite box art ever), the '71 and '72 Road Runners, and the '71 and '72 Chargers.