Years ago (like 28) I bought a 73 Duster with a stock 69 newport 440 in it and only a 484 purple shaft. It had very restrictive cut down log manifolds and a stock converter and a 3.23 Sure grip. With just a little carb and ignition tuning it ran consistent 8.30's in the 1/8th...which I think would be about low 13's in the 1/4. I remember fitting a Magnum manifold to the passenger side (nothing I could do on the driver's side) and just that one change was worth almost 2/10ths....

I also learned that 440 performer (this was long before the RPM) manifold was a completely worthless POS, the old CH-4b (I think thats what it was) was much better as was the Weiand Action plus.

I eventually put in a 11:1 451 stroker 400 with home ported 452's and the Bagshaw "pro Parts" headers and a 10" fairbanks and 3.91's and got it into the 6.90's (about 10.90 in the 1/4),....but to be honest it was a lot more fun with just the warmed over near stock 440 and quiet mufflers.

The earlier 67-69 440' shortblocks had much better compression. if nothing else swap the slugs with the HU-Cast KB's to improve the static CR. Also you can cut down the heavy 250+ gram pressed piston pins 1/2" and save about 50 grams per hole...you'll still have plenty of piston support but you'll also need to re-balance.

If I knew then what I know now I would have got a 4.15 MP crank and punched the motor .022 (4.342" = factory 400 bore) over and just threw in a set of stock 400 pistons on the factory LY rods and had a higher compression 493....with a lighter bobweight than the stock 440. apparently, Mopar had this little low buck secret in mind when they settled on the 4.15" stroke.....Hmmm, too bad they didn't bother to tell anyone...back then they might have sold a lot more of them. You could easily buy plenty of low mileage 400's out of the junkyard for way less than a set of new pistons.