In regards to the Sherman .... the M4 is not a cast hull variant, it is a welded hull. What you are referring to is the M4A1 Sherman. The early version has not been released in plastic, DML released what they called an early M4A1 about 6 years ago and it is now out of production. It was actually a mid production that did not have direct vision slots. I have heard no plans from any plastic company to release an early or from Dragon to re-release their mid.
Haven't heard anything on a Comet
Happy Modelling and God Bless
Robert