The military would have disposed of them as surplus in the original configuration - full wood, etc. Some people got them like that and did the "sporterising" themselves, some got a gunsmith to do it. "Sporterising" is the polite term, but it may also be called a "bubba" job, especially if the workmanship is poor, to suggest it would be the sort of thing an ignorant person with low standards would do. Some are done very well, some very not well. Some companies, e.g. Parker Hale bought batches of them and reworked them to sell as sporting rifles.
Typical modifications include original wooden stocks cut down, some had them replaced with new wood, (and at least two manufacturers still produce sporting style replacement stocks in plastic), sights may be replaced, some barrels were shortened, some actions have the charger bridge (lines up stripper clips for reloading the magazine quickly on the rifle) and/or rear sight mounts ground off and/or drilling and tapping for scope mounts, magazines may be shortened to reduce capacity or to fit flush with the bottom of the stock.