Looking forward to giving it a listen.
What as the spacing/angle between the Milabs and what was the spacing of the two pairs of omnis? In the photo the 4061s look very close together, but that could be the foreshortinging of the photo's perspective. Curious about the reasoning behind the close spacing. I suppose it could be a test of them mounted that way if that's the only way they could be mounted at other events without the spacer bar, but perhaps there are other reasons (like length of cables). Besides the differences between the mics themselves, the difference in spacing between the two pairs of omnis is likely to be a considerably bigger factor in the resulting sound than differences in preamps, recorders and cables. If you'd like to listen for the differences between the omnis by eliminating the spacing differences as much as possible you can simply compare one channel of each, listening in mono.
Two alternate mounting options which immediately come to mind would be to either mount each 4061 just above or below each 4006 to compare the two omni pairs most closely with identical spacing, or mount them something like half-way out the bar on each side to compare differences between two different, but more typical A-B omni spacings.