Worth the change?!

If it went 8.60’s in the Dart, it should go 8.70’s in the Duster as is. Unless you’re gonna zing it up over 5500 rpm regularly, the bigger valves won’t help any. Use the HP manifolds in the Duster, and get you some TTI’s for the Dart. I’d make the Dart the ground pounder, and the Duster would be the get in it and go anywhere car. Just my 2 cents....lol.