There are facilities at Eastleigh if the units are to be recommissioned whereas Ely is in effect just a yard, GC 180's did get work done at Eastleigh previously so maybe they are there for return to service works. GC maybe taking them on in the short term to release the 221's, perhaps GC have been told releasing the 221's would help their track access application to Cleethorpes?
Eastleigh would also be able to disassemble a unit if required. And with the 180s already 25-26 years old, can't at this stage rule out something like 3 of 4 stored units being revived, and the fourth unit being parted out for spares.
After the 175 reinstatement problems, it must be fairly obvious that not all parts will still work.
There must be an economic trade off between buying lots of new parts (some of which will be obsolete, so needing expensive special production), and alternative of accepting going to have to buy one unit outright and part it out, but then saving on new parts.