274/474 for stock 340

If you want a choppy idle get a cam in the lower 220ish range cut on a 104. I doubt you'll find a shelf cam that meets that criteria.

Going larger on duration will cause issues with low speed power output because the range goes up. Ignition timing and tune cna and will help a lot. Another trick is to advance the cam a bunch to gain back some grunt. Not the best way to do it but that's what I do with 284/292 cams in lower compression engines.

Unfortunately, you appear to want your cake and eat it too... Everything is a compromise.