Aikido 6GM8 - headphone stage

I am currently finishing a build of the 24V 6GM8 / ECC86 Broskie Aikido line stage amplifier and the space I have in the chassis is very minimal.

Is there a simple way to modify the standard circuit to allow for headphone use? For example, can we increase the value of the output caps (C3) to ensure the frequency response for headphones is adequate?