Hi Rolf!
The following is -opinion- not recommendation:
This would likely be an effort of love, not of investment. The few folks here that are capable of complete
cabinet restoration seem to concentrate on higher-end models for a reason (and work on their own smaller
projects for personal joy/interest).
-Replacing- a front baffle is difficult/significant work, one could fabricate reproduction cabinets ($$).
Or, if the front baffles are in poor shape, but capable of supporting the drivers with a clean repair/respray...
that would keep them much closer to being 'original', if that is important to the owner (and -possibly- more
value to a collector).
New grille/frames/foam(?) being required anyway, which I expect will not be inexpensive... another option
would be to keep them as they are, until suitable empty (or more restorable) cabinets can be located.
Just thinking out loud. Hope your friend can enjoy them in whatever form they may take.
-dave/grumpy