I'm tweaking a Lasagna Bolognese
The thing about lasagna is that it really only needs to be heated through.  All of the components (pasta, the sauce or sauces, the cheeses) are already cooked, or don't need to be cooked.

So baking the whole lasagna heats it through and helps the flavors to meld.  

A 4" thickness not tremendously thicker than some more traditionally proportioned lasagnas, so you should expect it to bake through in about the same time any casserole of that thickness would require.  I would start at about 325-350 degrees, for about 1 hour to maybe 1:15.   You may need to leave it covered for most of the baking period so that the top doesn't overly brown or dry out.

In the end, you can test the casserole with an instant read.  It should probably get up to about 150 or 160 F internally to be enjoyable

Lasagna should be very forgiving.