I only had a couple of hours to work on this today, so I make a relatively small amount but very critical progress. I am always a bit nervous with 40 year old chips, so after double checking the power rails, the 7220 bubble memory controller chip was installed and the system powered up. As a first test, base communication with the 7220 controller was confirmed with simple commands like read status, write data block to FIFO, confirm data integrity, etc. Seemingly minor progress, but a significant step.
One by one the remaining bubble support chips were installed, the board powered up, and temperature tested. All seems OK so proceeded to resistance tests with the dummy module. As seen in the photograph below, the dummy module is a PCB inserted in place of the 7110 bubble module.
The dummy module resistances and footprint match the 7110 bubble module, so while it will cause all sorts of errors, it provides the correct loading for all the drivers. After installed and its resistances double checked insitu, the module was installed and powered up.
So far all looks good so next time it is on to driving waveform tests and finally trying the 7110 bubble module itself.