340 Street Build

I have a very similar setup. 340, 4 speed, headers, Comp XE268 cam and 3.55 gears. I have a rather lumpy idle with the XE268, and I love it. I would assume the XE274 would even have a more aggressive idle. That should be an awesome engine. You'll probably want a 750 carb.
For the carb I have purchased a new Holley 770 Ultra Street Avenger to sit atop Eddie Rpm Airgap intake and ProMaxx 171 heads.

Do you know if Comp Cams designs their Chrysler LA cams specifically for the .904 lifter or if they just use a lobe design for the .842 Chevy or .874 Ford and call it close enough??

Did notice that Hughes Engines claims theirs are specifically designed for the .904 lifter and they advertise some kind of No Flat Cam Guarantee, if all parts purchased as a kit on same invoice. Only 60 days though.