High voltage gain block
You might wish to explore some standard audio power amplifier output stage topologies, rather then doing a class A design with a current sink at the bottom like that. 

A complimentary pair biased with a Vbe multiplier and a PNP current source seems to me to be likely to let you get pretty much all the way down (to within a few hundred mV of the negative rail), and within a few volts of the positive rail. 

Do not expect a particulary good high frequency response, Miller capacitance will be a nightmare with that rail voltage, and watch the SOA and second breakdown issues. 

There are useful ideas in Doug Selfs book on audio power amplifiers that look applicable to me (In particular some of the ideas on protection of the output stage are likely relevant).