Marushin XM177E2 and M16A1 parts compatibility

Apart from the obvious such as stocks and handguards/barrel lengths, are the parts from both models interchangeable?

I've got a semi complete M16 upper and lower with the solid stock but is missing most of the internals (ie lost/swallowed by dog/kicked under sofa never to be seen again etc) with a couple of other parts knackered and stripped threads.

I'm wanting to complete the build but change it to an M655 based model, hence my question about XM parts.