Any time a bolt is replaced, the issue of headspace arises. In most cases, the headspace will be OK or close enough that there will be no problem. In the worst situation, you could get case separation or even a blown rifle. One shot from a rest (the old "tie it to a tire" is not a bad idea) should show if things are OK or you could have a gunsmith check the headspace.
Those Spanish rifles were imported literally by the shipload; many were in good condiiton, but some were badly rusted with ruined wood. Few were in top condition or like new. They are not high priced even today, usually bringing $120-150. If they can be used "as is", they can be a good deer rifle, but most owners don't want to spend a lot of money on them.
Still, they are basically good rifles, and I have seen a few on which a goodly amount of money was spent, resulting in a very nice handy rifle.