The Sony a7RIII has been disassembled by kolarivision and there are quite a few improvements to improve thermals. Unfortunately, the a7RIII still has thick sensor glass so you will need to have the sensor modified if you want to use wide adapted glass on the camera. You can read the full step by step teardown here.
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Sony a7RIII: B&H Photo / Amazon / Adorama
Sony 24-105mm: B&H Photo / Amazon / Adorama