For one thing the B model used a relay to bypass the secondary of the mod transformer for CW the C model used a ceramic switch. The B model used a rely to apply primary power to the Low voltage supply and the C model used a switch. The B model read modulator current by metering the HV from the ps to the 811A tube plates, the C model metered the CT of the 811 tube filament transformer (a real worthy modification for the no suffix, A and B models)
Some books showed the final RF tube in the B to be a 4-250AX whereas the C called for the 4-400. The circuits were mostly the same maybe a few component changes, maybe around the keying tube. Not a lot of difference at all.
When you say, Dial Cover, I assume you want one for the VFO?
http://jmpalmquist.home.comcast.net/~jmpalmquist/Inventory.htm