Well heres a pic that may change your mind...

bunch of guys ramming the shell home with a pole?

a few more here:

landships 21cm Mörser m.10/16 article

Well that seems pretty conclusive! Just shows you how much I know!

Looking at the Landships pictures it's apparent the normal more of operation was with track pads fitted, shame these aren't included in the kit.
Steve

I doubt the chain track would have worked as a kit of parts or rubber belt, perhaps some kind soul will produce an etched set to complete the details on the model... failing that could always add a set of simple plates to the wheels with strips of plastic card joining them not perfectly accurate but should look ok