Contact the epoxy maker, usually the kind you are working with can be helped with raising to 150 degrees for a few hours which is pretty attainable with the method suggested

nothing on the expansion, it is what it is, the only thing you could do is keep the temp stable and not let it vary widely, you have re-bar in the casting right?

What does a 20 degree rise equate to in linear per inch? remember that for each cross- section of the casting epoxy is spaced apart with rock which has a different expansion rate so the overall change in length should be reduced wouldn't it?

Where in Cali are you? I'm in 1000 oaks