The answer is 'it depends'. What are you looking for? Is this bolted together? Can you assume it is one solid piece? Do you have access to SW simulation that will allow analysis of assemblies?
I think SW express only works on parts - if so, all is not lost if you are just looking for a baseline stress/deflection. In such case you could merge all the components into a single part and proceed. I'd suggest simplification and removal of bolts, etc.
Do you have a picture?