I didn't have time to post more than the pic before work today. You can see where one of the legs of the piggybacked IC is not connected to the matching leg of the lower IC if you look closely.

My thought is to look for a "double sided" 8MB 30-pin SIMM that has eight chips on each side of the type you're successfully using to net 4MB onto the MoBo.

Reverse engineer the addressing and control lines of such a SIMM will likely yield the information that will allow you to do the ugly Piggybacked RAM thing with some degree of confidence that it will work as an 8MB (onboard) RAM upgrade.

Putting a memory daughtercard underneath the MoBo is a far more elegant solution, capable of achieving vastly increased memory for very little money and less tedious wirework.