Deliver a 40kHz & >40V cosine wave to a transducer for communication
If you are going to use a class A amplifier on such a low voltage supply then might I suggest you configure the collector to drive a step up transformer. You can arbitrarily deliver what ever voltage you need to the secondary (within reason) but you might need some heat sinking on the output transistor.
The next problem is delivering a sine wave to the load. At the moment, the 555 produces a square wave and that’s roughly what you’d get in your current circuit (with or without an output transformer) so, you might be advised to use an op-amp low pass filter between 555 and the amplifier. You could use a pi network filter of course if you knew how to design it.
It’s unclear about how you would intend to perform OOK in the circuit but I would think that some logic input to the 555 and another transistor could be persuaded to give this functionality.