I’ll send you a unit for free. As a pat on the back.

Sure, I can give it a try. I'll send you a PM.
How much room do you have to work with? The HDMI board made by @Icky is getting ridiculously small these days, it might be the easiest fit once it's available. The only downside is getting the connector to the side of the case.
Vertical space is likely to be the tightest constraint, because I am trying to do all this without irreversible modifications, and without cutting a hole in the bottom of the battery compartment, there's only 14 mm vertical between the motherboard and the bottom of the battery compartment. If I cut the battery compartment, there's acres of space, but I really don't want to do that.
I did indeed read about your adventures there, and that was part of what made me think about giving it a go. I knew it had been a long time since your work, so maybe there was something better out there now. I don't yet know how good it will eventually look with the correct OSSC settings, but since my goal is not pixel perfection, but merely a good looking colour Stacy, I think it'll be just fine for me.
Having spent a lot of time poking through the schematics, I think the shadow chip is the only thing that's really different from an ST. Of course there are bits and pieces like the switch in the video connector, the trackball/mouse switch, and the specialised power hardware, but as for what's actually sitting on the bus, it's really just the shadow, and since its only job is to capture the same data as the shifter and convert it for the LCD, TOS isn't going to care about it or know about it. I think.We do know that the STacy has different hardware through, right?
Like the shadow shifter...for example.