Idle Rpm High in Park, Low in Drive

Invest in a 3500 stall converter and your drop in idle will disappear. Then Make sure the arm on the distributor vacuum advance canister has 8.5 not 11.0 Plug the hose into the carb above the venturis on ported vacuum after timing is set. Set the timing to 35 Total advance at 2500 RPM or higher with the hose unplugged, This would be where I would start and in that order.