How much does your Duster weigh? Let me tell you how radical my street legal 1965 Valiant 273 small block (2980 pounds) was to get a best ET of 12.72 at over 108 MPH:
10" M & H Slicks (29" tall with 10 lbs air pressure)
Super Stock leaf springs, pinion snubber, frame connectors
Cyclone fenderwell headers (not equal length)
4.56 rear end
4 speed (launch and powershifted @ 6000 rpm, 6400 traps rpm)
.580 lift 312 degree solid lifter camshaft (Isky at the time)
10:5 compression pistons (balanced and blueprinted stock block bored .060 over to 282 CiID)
Stock cylinder heads "ported and polished" with a Dremel tool on the kitchen table.
600 CFM Holley Double Pumper on Tarantula Manifold
electric fuel pump, trunk mounted battery, fuel cool can (for ice), no power accessories
Your big block should be able to match this performance if it is modified in a similar fashion but I believe you have a long way to go still. Have a blast and let me know when you break into the twelves!