stamped steel LA rocker arms

It seems to me that you'd wanna tailor the rocker arms used to the cam you have, but also take into account the heads you're using.

I'll be using ported 'O' heads on my 340 and, as far as I can tell, they're the 340/360 stock pieces.

That said, if the 273 pieces work better for your particular build, by all means, go for it.