The factory stroke for a 383 is 3.38. Relatively short for any big block. Point is, rpm's are required.

My 69 Rr ran 13.79 at 102 with a 3.91 gear. This had a 284/484 cam, TM-6 single-plane, 750 AFB, closed chamber "door stop" 516's with the 1.60 exh.valve.

I added the 1.74 exh. valve, template/bowl ported the heads, 3" exhaust and went to a 4.30 gear. 13.08 at 106. A crappy 1.99 60 ft.

This was all with an unknown seriously ragged on shortblock. Factory Mopar HP motors didn't really have the compression as advertised. Good compression makes a better air pump at ALL rpm's.

Personally, I'd do the 3.75 RB crank stroker deal to work with your 3.55 gear. ALSO, check into what guys here refer to as a "quench" motor and make it a priority. Then you can manage some real compression...........hence, power.