I don't see any SRAM for L2 cache on my two NuBus adapters for the IIsi. This may be a red herring again.
There are two IC's not well labeled as U2 and U3 on the silk-screen layer, it almost looks like it says L2 and U3. However the ICs are ID'd in between as 74ALS240, which is an Octal Buffer, not SRAM.
I know the NuBus ChipSet on the board has no built in SRAM, because the DuoDock uses the same ChipSet and has discrete SRAM L2 Cache on the Main Logic Board. It'd be an interesting experiment to see if this Cache works with no DeclROM in the Dock.
Someone likely read the abbreviated U2 designation as L2 with a serif on the L as opposed to a shortened riser on the right had side of the U, which looks a lot like a mirror imaged J.
Or I'm way off base once again. But his is the first mention of cache on the NuBus Adapter I've ever seen.
I haven't given up on hacking L2 Cache into the SuperIIsi™ just yet, however. You can probably figure out the intended source for compatible SRAM . . .
. . . and the rough model for adding that cache to the 68030 PDS! [}
] ]'>