my 66 gto has numbers matching block but not top end. 4 barrel car. it also has old 70s repaint, wrong color. i found a wrecked 66 bonneville with 421 tripower. money wise is it worth it to put in the gto. i know set of the pants and silly grin wise it is. $3000 for bonneville posi 12 bolt rear, runs and drives. i would pull what i need and let go the rest.