Hi Tom,
The chassis would remain the same.
You would just need to procure MSA 2050 controllers.
SFP modules of MSA 2040 and MSA 2050 are identical as per quickspecs.
MSA 2040 quickspecs page 29:
https://h20195.www2.hpe.com/v2/getdocument.aspx?docname=a00008276enw
MSA 2050 quickspecs page 21:
https://h20195.www2.hpe.com/v2/getdocument.aspx?docname=a00008276enw
MSA 2050 controller - Part number: 876127-001
The only upgrade document that I could find is listed below:
https://h20195.www2.hpe.com/v2/Getdocument.aspx?docname=a00015116enw
You may consider booting with just MSA 2050 controllers with out any hard drives installed in the chassis to ensure that the controllers are at latest firmware version VL270.
Note: Linear vdisks to Virtual Pool migration is not supported.
MSA 2050 supports only virtual pools.