No, they're not all the same.
The bolt patterns and magazine box inlets in the stock will vary from short, long, and magnum actions. Some calibers are "small shank" and some are "large shank". Most custom barrels that are readily available are only large shank. Their target "custom" action is a unique bolt pattern as well.
So you have to match up the action size with the cartridge and COAL you want to shoot. My rule of thumb is to just get a large shank action in the length I need, even if it's for a 223rem. You can always fit smaller cartridges in large shank actions, but the reverse isn't true (can't always run short action cartridges well in a long action, for what that's worth too - and of course a long action cartridge won't fit in a short action). Then you have to get a stock with the right inlet, or buy it with the action - keeping in mind that if you go from a sporter profile to a heavier profile that you'll need to inlet the stock for the large shank and larger barrel diameter.
If you want anything other than a standard SAAMI chamber (tight neck, longer throat, etc), then you'll need to know that before you order your barrel as well.