Actually I think I found what I'm gonna go with... Stereo Integrity has their whole lineup on sale right now, so I think I'm going to grab their M25 mkII tweeter, M3 carbon midrange, and the new TM8 8" midbass. Physically the TM8 is almost the same diameter as the Focal ISU 200 8", but about 4mm more shallow so even better. And with an Fs of 58hz, this thing will play pretty low. The M3 midrange was pretty well reviewed by Erin (Erin's Corner) and dimensionally should fit without issue in the dash (don't care about the rear doors), so I'll just use 2 and disconnect the middle of the three mids. The M25 tweeter is about the same size as the Scanspeak D3004, but about 3mm smaller diameter.
Regarding the tweeter sail panels, Travis Llado made some 3D-printable sail panels for his Focal Utopia M tweeters (
Free CAD Designs, Files & 3D Models | The GrabCAD Community Library), so I might take a look at that and see what's up.
Now to get this whole harness situation in order...