Panel mount IFR GPS for training ...

No, you do not need an IFR GPS to get your instrument rating.
Roy makes valid points.
I would add that you would actually be better off with GPS while you do
your training.
My reasoning is that it will teach you to think about where you are in
the 3-D world instead of showing you. You will have to think to
interpret your instruments and convert them to a point in space based
solely on how the NAV needles are moving.
Once you can do that, then add the GPS.