Are you using the right description term here? Are the inserts really cupped, or just sunk? I understand cupped inserts are common in other makers EM's of this era, but I have rarely see a 70's Williams with cupped inserts. Sunken, yes, all of the time.
If this is the case, just remove the inserts with a heat gun or blow dryer and then reset with superglue gel and press flat. It will not take you too long to do and the results are very acceptable.
Watch this series of videos on youtube. 4 parts. I have had great success using this