The Redding bushing dies you are buying are a *great* piece of kit. I use them to make my .308 match ammo.
Just in case you don't already know this, you only need to buy a .30-06 sizer and a .30-06 seater, you can load both .30-06 and .270 with them. This is because the .270 is simply a modified version of the .30-06 case (it's just necked down). The .30-06 seater will work with both. In your neck sizer, all you need is a bushing for your .30-06 and another bushing for your .270.
If you don't already own a full-length sizing die, you will want to get a "body die" in .30-06 and also in .270. A "body die" is the complement of a neck die, it sizes every part of the case *except* the neck. If you size a piece of fired brass (even one that has been fired in another rifle) in a body die and then in the neck die, that is equivalent to having sized it in a FL die.
Using these bushing neck sizing dies is a bit different than using ordinary dies with an expander ball. Dies with an expander ball will correctly work on pretty much any piece of brass. The way that they do this is to first make the neck too small, and then drag the expander ball (typically .306" or .307" diameter) through the neck in order to make the inside diameter of the neck a consistent size that is just enough smaller than the bullet diameter (.308") to give good snug neck tension. The tradeoff is that the brass is being "worked" more than it needs to be, so it will wear out quicker (the necks will eventually work-harden and crack, typically after 10-25 loadings). Also, the case mouth usually needs to be lubed so that the expander ball moves easily and doesn't bench the case necks, giving you crooked ammo.
In order to make good ammo with these dies, you need to have cases that have consistent neck wall thicknesses. This is because all you are doing is setting the *outside* diameter of the neck (based on the bushing size that you choose), whereas the amount of tension on the bullet is determined by the *inside* of the neck, which will vary by exactly the amount that the neck wall thickness varies.
There are a couple of ways to get consistent neck thickness. One way is to neck turn your brass. This is a lot of work, though fairly simple. You need a $35 (or is it $50 now) neck turning tool, and it'll take a minute or so to do each piece of brass. Figure on spending a couple of hours (once) setting up to turn the correct amount, it's a pretty fussy adjustment (if you trim too much off your necks, they will be expanding and contracting more than they need to each time they are fired, so they won't last quite as long).
Another way to get consistent neck thickness is to find some consistent brass. You can do this by trying a lot of different kinds and doing lots of measurements (having a $100 "tubing micrometer" is not essential but it will help). The lazy man's method, which I subscribe to, is to just buy a bunch of Lapua brass. It is more expensive than Remington/Winchester brass (though it is less of a premium now that it was several years ago), and I have found that it is consistent enough to be a "no-prep" solution. Buy the brass, and use it - no neck turning, no case weight sorting, so primer pocket or flash hole work, etc.
If you are going to make a mistake on your neck tension, it is much better to have 1 thou more than you planned rather than 1 thou less. Unless you are extremely confident of the consistency of your brass, and your measurements, I would recommend that you shoot for a bushing that is 2 thou smaller than your loaded round of ammo (or even 3 thou smaller as Ganderite suggests).
(When I bought mine, I got two bushing, one .001" under and one .002", just in case.... though paying $15-ish for a bushing you *probably* won't need does make my Scottish blood curdle a little bit)
One very nice thing about neck sizing in this manner (consistent brass, bushing dies) is that you don't need to lube the cases at all, which makes things neater and quicker.