How to drill into an acrylic tub to create an overflow drain
I would buy a piece of acrylic plastic to test with (you can sometimes find that with window glass in home improvement stores, or at a arts &amp; crafts store).  Then place some masking tape on the front and back of the test piece, and use a ceramic drill bit.

Then if that goes well, hopefully it will go well on the real tub; but if there is an inconspicuous place to try a small hole (maybe the back foot if it is a footed tub), try there first.