Damper Doctor takes OEM dampers, presses them apart, then replaces the elastomeric material and presses them back together, clocking them properly so you can properly time the motor.

They show a 7" damper for a 396/402/427. There is an 8" damper listed for a 427 that would work with a different timing tab as you said.
Here's the 7"....
http://www.damperdoctor.com/Merchant...egory_Code=CHE
And the 8"....
http://www.damperdoctor.com/Merchant...egory_Code=CHE