^^Right, when you hear carbine length buffer tube, buffer spring and buffer, they are referring to the collapsible carbine stock.
When they refer to a rifle length (A2) buffer tube, spring and buffer they are referring to the A2 stock your wanting to use. You can use pretty much any barrel with either.
I had a .458 Socom for a spell, I imagine it's probably pretty similar cycling to the 450. I only ever shot 40rds through it and I was running a collapsible stock. I ran an H3 in it with an adjustable gas block.
So I think BurnOut's recommendation of an adjustable gas block and H2 buffer sounds like a good start. You may have to experiment with the adjusting the gas block to get you where you want to be.
I use Geissele buffer springs, you will need a rifle length buffer spring so you may experiment with different ones over time. I have a few Sprinco but for most I settled on the Geiselle. The Tubb flatwire is supposed to be a good spring too, I've just never tried one. But I wouldn't hesitate to.