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If you have the money to build it the 400 would be my choice over the 383. However the 383 will walk the dog on the 400 in stock forum. And by this I mean a 68 or 69 383 versus a 72-73 400.
Here are some first hand facts of cars I owned that I'll share:
'68 Plymouth Fury Police Package. 383 Commando factory dual exhaust all stock except the heads were redone with harden seats. 3.23 gears. Weight, 4150. Best ET as set up 15.19.
'89 D150. 400 2bb, I added 4bbl and headers. Nothing fresh, ran as pulled. 727. 3.21 gears. Weight about 3850. Best ET 14.5 as it sat.
Pickup a little lighter and had headers. Almost 7 tenths faster so weigh out the odds and see what ya think. That 400 changed how I felt about 400's. Later my brother added a 750 holley DP/Weiand Action Plus intake and 3.55's to the Fury and ran a best of 14.7's