Intake choice.
Well my county goes from 4300ft. to 10800ft. so that is a big variable. Not stroking it. Would be a street car.
This might be problem; depending on your expectations for the 340.
If performance is on the table, that elevation change is gonna be a big problem.
From 10,800 to 4300,is 6500ft.
With a very modest cam, that has an Ica of 58*, and at an Scr of say 10/1, that elevation change represents around 30/35psi cranking cylinder pressure. If 10/1 creates 150psi @ 4300, she will be down to 116 by 10,800
That 58*Ica, is a pretty small cam.
Typically, a guy will install something around 66*; Don't do it!
To get pressure of say 160psi @4300, with an Ica of 66*, would take a Static Compression ratio of ~11.2....... but at 10,800 she will be down to 126psi, and feeling pretty lazy.
Even if you stall it up, she'll still be lazy.
As a street car with an automatic, my guess is that you will be running 3.23s; which, this too will be a problem. With a cam that has a 66* Ica, the power will peak somewhere around 5200. Which is; 47mph in First, 80 in Second .On the 1-2 up-shift the rpm will drop from say 5500 to 3250. But the power doesn't start until ~3700, so, without decent cylinder pressure, even at 4300ft elevation, the poor 340 is wheezing....
never mind at 10,800ft.....
If it was me, I would be thinking about a bigger engine or a stroker.
Jus saying