Assuming that you are adding cases rather than just adding variable, you can use the RENAME subcommand on the ADD FILES command to rename variables in each specific file. If there is a pattern to the names across files, it might be possible to automate this renaming, but otherwise you would have to spell out the mapping.
ADD FILES allows up to 50 files to me merged in one command, so you would need to do two passes to get all 70 files together.
Note that if there are string variables in the files, the lengths must be the same for each particular variable across the files. If you have a lot of that to deal with, the STATS ADJUST WIDTHS extension command can fix that problem.
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