Also, is it possible to retrofit the seat memory feature into the passenger seat with associated buttons on the passenger door (by for example using Chevy SS parts)?
I've seen the individual parts available from 3rd party Holden parts suppliers. The one part that is elusive is the seat lower frame. Most people are recommending scavenging parted out frames from Calais/Caprice etc. My only concern is that the loom is not available on the SSV-R. I am lazy, I haven't looked to see if the plug is there. I was hoping someone else had forged that trail before me. But, I haven't had a solid response on several forums.
I know for sure, though, you can get the switch block, side cover etc from online parts suppliers. So, if our cars have the loom, it should be fairly easy.
I cannot comment about your seat foam question, but I know of many places (at least in QLD, VIC and NSW) that are retrofitting SS seats as HSV, using the same pattern and similar materials (also allowing customisation) whilst reusing the SS seat, airbag and frame.
Soon, I will be having my seats remade as HSV GTS patterned foams with a diagonal pillow-stitch cream on black leather with black on black Holden emblem embroidered into the headrest.
You can even specify the density of foam, for example; heavier, more resistant foam on the thigh bolsters.
Pricing seem consistent too, about as much as people are currently asking for wrecked genuine seats ($1600 for fronts, $900 for rear), which is a good deal if you want customisation, like me.