Ronald,
There is one fact that you nor anyone else can disregard. If the G1 pyramid was built around the coffer as you and everyone else agrees, that requires the coffer to have been constructed before the pyramid was finished. If you want to narrow that down you could say that the pyramid was built to what ever stage was in progress at the level of the kings chamber. Lets assume then all the granite used in the kings chamber was being quarried at or around the time that the granite coffer was quarried, why then are they two different compositions of Aswan granite? Why then are the chamber walls set so perfectly and polished and not the coffer. IMHO, the chamber was first constructed on the ground outside of the pyramid, the accuracy achieved requires such attention, once the stones were carefully cut on their joining sides they were moved up into the pyramid. It would be at this moment that the coffer would have to have been put in place.
The surprise is that once the coffer was installed, the workmen set to task; smoothing and polishing of all the wall stones (...), during all this interior and of course the subsequent exterior work on the pyramid nobody wanted to properly cut, polish or ornate the coffer, no they decided (khufu decided) the walls of the chamber were far more important than his unusual and characteristically archaic granite coffer. It was then, as if the house (chamber) was more important than the occupant (coffer) it was built for. This is at its core extremely contrary.
Because the coffer found in G1 was placed inside during construction one would expect to see that the Aswan granite used in the pyramid would match that of the coffer, but they are different. Additionally, one would also expect the craftsmanship and over-all characteristic of the coffer to be contemporary with all other stone coffers of the 4th dynasty and the least of all with the actual contemporary walls of the chamber it would rest in, but it doesn't.
I.E.S. Edwards postulates that there were two coffers, the first one (properly adorned) was damaged or lost in transit to the location, subsequently the workmen had to rush and build a new one in the rough to replace it. This is beyond speculative, its complete fiction and his only support for the claim comes from a late New Kingdom oblisk that was abandoned after it cracked in transit. I would imagine, since all the craftsman shops were at the site preparing the stone delivered from the quarries, that the coffer would also be fashioned there too...contemporary with all the other stone fashion.
The coffers characteristics and the limits imposed by its internment force a conflict between the employed abilities of the work-force used to build the pyramids interior and those who were responsible to build the kings coffer.
Lastly, none of these attributes refute the possibility that the coffer in G1 was recovered or taken from an older tomb, a trend that characteristically stands out. It is quite possible that it was seen as a valuable relic they decided to use in the alchemy process of the pyramid. Because an older style small step once existed under G3, the construction pattern of the cut-out passages from the original 'archaic' chamber, and because it has a floor recess for a missing coffer that remarkably accepts the 'out-of-place' G1 coffer, I believe consideration should be given to the idea that the G1 coffer may have once been the missing recessed coffer in G3.
Best Regards,
B.A. Hokom