I find it strange that the #96 car drove back to the trailer under it's own power after qualifying. It was parked in the corner of the tent and it never moved from that position. I have worked on many dry sumped motors (the M3 motors in Cup are dry sump) and know that if the belt comes off, the block will have a hole introduced in it. This only takes about 5sec of running.
Plus, there were many M3's at the track and I doubt that it would take very long to change a motor with top notch mechanics. Turner was able to change two motors in their ST cars at Barber without a problem. They only had one spare and a fellow competitor lent them their spare.
One other point. The 996's and 997's are the most stock cars in the GS class. The M3 is next in line, as it is allowed bigger front brakes and a dry sump.
Read into this all you want but something is strange about this whole situation.