The mPCIe Quad SATA card arrived. Installed and tested with two drives attached (I will post screenshots later), it worked out of the box, no driver or kext needed. Proceeding with the lift kit, I have to figure out where to relocate the fan, maybe make a exhaust port left of the dual eSATA ports. This is on 10.5.8.
The online 3D models of the ATVg1 did not match the actual device.... That led me down a long slope of G3 Surface Continuity that took way too long. Instead of trying to calculate such a curve, I compared an AppleTV gen 2 to most other Apple devices and they all have nearly identical curves, just separated with longer straight surfaces for larger items (even lines up on a 27" iMac).
Imported a photo of the ATVg2 into Illustrator and matched a curve and exported to my 3D model. Adjusted and did a test print in gray. This is upside down of course. Final will likely be in white.