There's no reason why not if your uncle could have done it himself assuming the ability and know how. You would be acting under the power of attorney and not as a financial adviser, however. You can't do that without the usual registrations as you know. But you can act as an individual under the POA. Happy to discuss further. I hope that helps. Please leave a positive rating so that I am credited for my time.
I don't mean that your uncle would have been able to do the work. I meant that if he could legally do the work then you can do it as his attorney. You can only get paid if your uncle would have paid you were he able to make that decision for himself. A family attorney is not normally entitled to be paid otherwise. However, as you were a qualified advisor you would perhaps be entitled to be paid at the rate you mention but you certainly need to get written permission signed by the other attorneys.
I think your approach is fair and I wouldn't envisage any difficulty if everyone agrees.