No, those values are too low. 100 ohms won't help enough. And the volume control already acts as the trim pot (in a way) so adding another doesn't help much, even if it is the correct value.
I don't remember the exact values, but I know the resistor (not the pot) needs to be a pretty high value, (ohms) and I believe it should be a 5w. Years ago (40?) I got detailed instructions directly from Wurlitzer on how to do this, but somehow, during a move, it got lost. I really wish
I could remember the values.
Do you want to completely eliminate the headphone jack or take a signal from it and add a second jack somewhere? I personally would add a second jack.
Also, be sure you piano no longer has the "death cap". If there is any stray voltage coming out of that jack, you could fry whatever you are connecting to.
(See previous posts regarding the "death cap")
And of course, you are adding any resistors in series between the + (hot) wire and the output jack. You are not adding resistors in parallel across the + and -, this will short out the amp. (If a resistor is too small, it could short out the amp)