I was at the store last night and just happened to walk by some original Intel PII heatsinks I thought those would work nicely with those little 5ish Watt SoC; low profile, light weight and a quiet fan. I'm a little concerned about the extra weight my HU is a slim type all the electronics are sitting vertically. The road vibration and heat in a car would put a lot of strain on those 2 little mounting screws and there's only 3 dabs of silicone holding the connector in place. They should have put at least 1 more screw on a different plane to really secure the SoM.
Can't say much good about using a cast shield as a heatsink either. What is that material, recycled aluminum. Probably not the best for heat transfer, the pitted surface definitely is not. I hope they used a heat transfer pad between the SoC and the shield and not silicone. I'm sure it's all good enough but it's definitely not meant to last long.
in my case, PX5 board is orizzontally mounted, so the heatsink weight is don't care.