An alternative is our patented tool-less gas block called the Govnah by MicroMOA.
As seen in the picture below, you don't need any special tools to move the regulator plate. Just push it through an opening on your rail system with a bullet or any other object you can fit through your rail.
Unlike the Switchblock, the Govnah is modular so you can configure it to your exact configuration from no port to any port size you want to drill if one of the pre-determined port sizes aren't to your specifications. Picture below shows some of the various plate regulator options.
We currently only offer 5.56 pre-drilled plates while many use it for other calibers including .308. The issue is so many variations in the other calibers that it is hard to pre-determine what you will need but I know a 20" .308 will definitely need port sizes larger than what we use for several of our 5.56 offerings so it is just a matter of making ports bigger...always easier to take metal away than put it back.
Also, unlike the Switchblock and all the other tool-less adjustable gas methods currently on the market, the Govnah is the only one that uses standard un-modified gas tubes.
Below is a picture of an LEO's AR10 build with Govnah installed.
More info, pics and vids on my site:
MicroMOA - Home of the Govnah - Modular Adjustable Gas Block
Thanks!