AutoX,

I agree but the intake closing event with a good HR lobe combined with a smallish (but adequate) carb Venturi and a VERY good dual plane, you will be streetable. )Acceptable manifold vacuum in gear no lugging in the 35-45 range in high gear, that's my definition of streetable. The RIGHT cam can lope at idle and be Plenty streetable too, IMHO.

I would venture to be a little milder you could knock the cam down ~ 4-6 degrees @ .050 and go to a 2800 stall 10" vert with 3.55 gears and still be right in the 400 range and that much more streetable....if I built it anyway

A blueprinted 340 can make about 310-315hp, especially if you use the '68 only manual cam profile advanced 4 degrees. And that's with a too small carb and an undersized intake manifold cross section. Back in the day the old LD340 and a 68-69 440 AVS of a New Yorker and a distributor spring tweak was a Huge step up on a 340, maybe 35-40 hp with no other mods...except you needed new valve springs if it was an old long block.

The old Ultradyne 231/239 @.050 hydraulic is a beast in an otherwise stock 340 stick A body car with good valve springs.