I bought one of these NIB four years ago and it had the v3 ROM but I sold it ….
Any chance you can get in touch with the buyer?
@Erik Can you take a bunch of really good shots from different angles and take measurements of that chip clip for me?
The Radius guys were key Macintosh Developers, I wonder if that Radius16/Plus ROM contains, supersedes or patches the Plus ROM? His Steveness was long gone by then, the DTP revolution was in full swing and saving the ass of the Macintosh. The Plus was the machine that industry was waiting for and Apple's stop gap offering during SE development.
So I'm wondering if any bits of the crown jewels lie therein? That would handily explain its incompatibility with Radius16/SE ROM.