I had a similar issue with the 318 that I rebuilt in the Duster. Pretty mild combo, 4bbl intake and carb, Comp Cams 224/224 @.050 with *302* heads... Nothing major..
Basically, started the engine up once it went in and ran in the cam, ran OK on idle and then went put in Drive it would die. Event with idle turned up it was hard to keep it running..
I checked a fair few things whether it was the Carb or hose vacuum leaks. In the end did the WD40 trick around the intake and found I had a massive vacuum leak on drivers side intake. Off with the intake (crappy tin gaskets that were there) new set of Felpro composite gaskets and intake back on and she started fine..
