Dear Unmesh,

it would cause a real problem to you, when touching it... Such a high DC voltage is absolutely killing you, please be very careful!!!

First, I would try to get dependable information how this shunt is connected relative to earth potential. If cold end has some hundreds of volts I would proceed with contactless methode. Equally what anybody in company would tell me. It's not trivial to have good isolation at such voltages for longer periods.

If on the other hand cold end sees earth potential, I would use an instrumentation amplifier to amplify 75mV. Both cables comming from shunt should be connected via many kOhms to ground of circuit. Also, some filtering and protection circuit should be included. Time constant can be choosen to be very high. Behind instrumentaion amplifier you can put VCF.
Connection to other equipement can then be done directly, not necessarily needing an opto.
0V of circuit sees earth potential via load resistors at the input of instrumentation amplifier. When this circuit is connected to other equipement there will not be any problem, either when 0V of this equipement is also connected to earth or not. Having here some connection of 0V to earth would be advantegous.

Bye,
Kai