hi alec,
I have tried some Spice to LTS conversion in the past, but I found I got so many errors it would not run.
Did try editing out some errors , but no luck.
What I tend to do now is to create a hierarchical model of the OPA using the diagram and component values from the datasheet.
If you choose a Linear devices OPA having a similar specification to create the model, the performance will closely match the original IA.
For the INA128 , look at the LT1167 listed in LTspice OPA options, its a close fit for the INA128.
If you need a hand with the model just ask.
E.