Age old Creaking Tub

You’ve likely heard all this before. I’m renovating the family bathroom.

I deleted most of this post and will add new information in next post, would appreciate comments.

Okay so I've pulled tub, American standard, circa 1988.

Now I can see issues. First the ledger across the back is dead level. It is placed 15 1/4" up from floor. While tub is level left to right it falls back from front and water collects in corners.

The drain face sits 2" above floor. The floor running from front of tub to rear is very level. The floor running left to right has high spots at the joist and at the very left end, drain end, the floor is depressed. Likely used studs just a little long and forced them to create wall.

So as I understand it I have to make front edge level and complete, no sags. Problem is how?

Next I think I should add to ledger. My initial assertion was to add 1/2" there by making ledge at 15 3/4". This should make tub level in all directions which I understand is a requirement. Now I suppose how much I add will be based on how much I add to front to make level.

The drain is loose and I can easily lift 1/2" but don't want to lift so high that the face is on an angle.

So the leveling across front has to be solid, (don't want it destroyed as I single handed replace tub), but not add significantly to height.

Any recommendations on what to use to level front? Compounds, materials etc?

Thanks

So if you happen to be following along.

Instead of adding leveling compound to make front of tub level I used a belt sander and carefully removed high spots. Still have a little low spot by interior wall. This can be addressed.

So instead of adding, I subtracted.