I've been looking for the most convenient way to preserve stock at room temperature. It seems that Bovril preserves just containing a 14% of salt, while every powdered product contains 50% of salt. I was wondering why so much salt is needed for powdered stock and if it's safe to try this kind of preserve at home.
If you are starting with your own beef stock, the best way to preserve it long term is to freeze it. If you are lacking on freezer space, reduce it by half...or even three quarters, then freeze. You can add the water back when you thaw and use. If you concentrate it a lot, you can even freeze in ice cube trays for convenience. This will be far superior to any bullion cube (like Bovril, which has very little relationship to stock, and BTW, 14% is a lot of salt).
These commercial products are using dehydration, salt, and other ingredients to create an environment that is inhospitable to pathogen growth. The flavor likely does not even come from stock. You are probably not able to reproduce the industrial process that they follow.
I would suggest your time is better spent making a good stock, and following my suggestion above. Your food will be better because of it.
You can preserve liquid stock at room temperature using pressure canning, where you put your jars in a large pressure cooker to raise the temperature of the food you are preserving high enough that it will kill all foodborne illnesses. This is how low acid-low salt foods like tomatoes and beans are typically canned and jarred. Pickles and jams can be water bath jarred because they have enough acid, sugar and salt to act as preservatives. You can't water bath stock because it doesn't have enough salt, and if you added enough it would be absolutely inedible.
I would first reduce the stock down to make a concentrated stock before canning, it's less work overall - as you get more stock per jar and can use smaller jars there's fewer batches. Add to that it takes less shelf space.
I would only can stock if freezing is not an option, if it is I'd use the method @moscafj has outlined, it's faster and far easier.