firebird, match the cam to your static compression ratio. If you don't know what pistons are in the motor and what the deck is (piston crown to block surface at top dead center), wait until you get the heads off to measure it. You also don't know whether the pistons are flat top or dished, so wait to order the cam until you can figure the compression ratio.

I assume that by "good sound", you mean a lope at idle. Having a lope does not necessarily mean that you know what you're doing when choosing a cam. There are a lot of posers out there who install a cam that is too wild for their otherwise stock motor just to impress the geeks down at the burger joint. This usually results in very low manifold vacuum which will not support power brakes and a loss of low-rpm power. You already have a good understanding of power range.

Many motors have been rebuilt using the old rockers and pushrods. I don't do it anymore because these parts are relatively cheap and I'd rather use new parts that can lap-in together and be happy with each other. You'll be using new lifters on the new cam, so I recommend new pushrods. You might get by with the rockers if you inspect them closely for wear and cracks. Don't re-use them if the valve stem has worn a trough in the tip of the rocker.

Any cam you purchase will have a "window" of operating range of about 3,500 rpm's, so they're fudging a little on the description you posted, using a 4,000 rpm window. Depending on how your compression ratio turns out, that cam may be a little too mild.