I'm appreciative of the project.
Some impressions:
1) without the belly pan we might be looking at a Cd 0.035 penalty.
2) compromising the diffuser, due to the missing belly might add another Cd 0.02 penalty.
3) lack of rear skirts could mean another Cd 0.0.006 penalty.
4) and since a 'fastback' body is the most aerodynamically sensitive to tumblehome, there's a little extra fruit there for the taking.
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All of which adds to build complication and expense. And outside the scope of the project.
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The 'skirted' configuration reflects an aggravated frontal area situation, so whatever the Cd was, it would be a little lower, if adjusted for the higher Af.
I give it all a big thumbs-up!
Thanks again for sharing it.