What's under those tiles? If it's old plaster or sheetrock in any form it's very likly your going to regret not doing this right and removing all of the old tile.
No floor is ever perfectly level, the tub it's self is not going to be perfectly flat and level.
If there's nothing to 100% fully support the tub it's going to flex, flex = cracks in the tub, cracking caulking, can cause the drain fitting to leak.
In an older home it's also all most always advisable to replace any old steel supply of drain lines, and the old control valve.[/quote]
Yes, it is sheet-rock under the tile (studs, sheet-rock, and tiles) however what am I going to regret if I "don't do it right". There is no mold, and the sheet-rock under the tiles I removed to get the old tub out was solid,. no water damage. As mentioned, all of this is to be covered with a full acrylic tub surround, so I don't see what the issue would be leave the old tile and sheet-rock intact?
My floor must be one in a million. as the tub seems flat, and level temporarily installed as it is. Forgetting about replacing the sheet rock for now, (I may consider it) what about gluing the feet to the floor if I don't replace it and cannot access the feet.. Is it necessary?
The drain and over flow are brass, connected to and ABS trap and drain line. I will replace the brass with ABS as the overflow is higher in the new tub. I don't have a control valve, unless you mean the tub faucets, which I am keeping.
Just found this Need some help on installing an acrylic Bathtub
Not my pictures, but exactly what I have done so far, and my new tub fits in the slot. You see I would not be able to raise the tub to get the glue under it.