Worth the change?!

That 268 cam isn't making any power above about 5300-5400 in a 360 like yours. You're just killing it with RPM. Shift at 5300-5500 maybe 5700 and see if the car picks up.

Had a similar set up in a 71 demon, it ran 105-107 mph in the 1/4. Never shifted above 5600.