Hi,
Still have it. But it's in our summer house / cottage so I wont get there until a week or two from now.
You don't need the dimensions of the old panel. Because it is not resting directly on the cabinet. It is resting on the two bolts you remove from inside the cabinet. With these bolts you can adjust the position of the Panasonic panel.
So you actually have at least 1 cm. more than the frame height of the Panasonic panel.
But we can do some reverse engineering. I put a LG42LS560T in there. I put two small blocks of rubber beneath it to rest on. The rubber was approx 1 cm. thick.
That positioned the LED panel 3-5 mm. below the speaker cover. The aluminium frame will also cover approx 3-5 mm left/right/top.
If you look at some pictures of the LG you get an impression of the space you'll need.
If you go for a max. 5 year old donor I doubt you'll have issues.
On the other hand. It will take you 2 minutes to remove the Aluminium Frame of your own BV5 and 2 minutes to remove the speaker cover. That will give you the possibility to measure...