Was wondering the possibilities of a twin cylinder Zilla motor.. I mean there is triple cylinder banshees, why can't we have a twin cylinder 500 motor!?!? I sure would love to have one!! May have to do some research on some machinists

A twin cylinder engine of that size will have a balance problem.  A huge counter balancer can be added but will only be a band-aid for the rocking couple that is inherent with any twin cylinder 180 deg engine.

Ask some of the guys that have spent thousands for the custom Matoon cases and the CP 1000cc twin cylinder kits why their drag frames will not last more than a few race days.  Ask them why their engines are constantly siezing because the vibration foams the fuel in the float bowls and leans the mixture.  Ask them why the vibrations aggravate the vegus nerve in their chest and their heart rhythm is altered and paralyzes their diaphragm so that they cannot breathe.

A twin cylinder's rocking couple gets worse as the distance between the cylinders is increased and the piston and rod assemblies become heavier.  The weight of the components and the distance between cylinders has to increase as the displacements of the individual cylinders are increased.  Machinist can build large displacement two cylinder engines have but will not be able to overcome the basic design hurdles inherant with the 180 deg twin cylinders.