I wish I hadn't seen the picture of your tub before I went to bed last night. The thought of it interferred with better dreams. To gain a shower you need to have a side wall built with a valve, spout and shower head. The problem is the drain. Do you have access below this neat floor? Todays overflows come down next to the inside wall of the tub or in your case inside the walls of the tub and the drain shoe connects to the drain above the floor. I think you will have to replace the tub.
It’s a raised house with crawlspace underneath. A local plumber came out and advised leaving the old plumbing alone and installing a new shower valve in the existing wall on the other end of the tub. I’m just trying to make the house rent-able for a few years before tearing it down. Thanks.
The only easy way is if the spout which is where most tubs have their overflow has a standard 1/2" thread. Then you could mount an Alsons or similar hand held. That tub style is why the codes were changed to require the end of the spout to be above the rim of the tub.
You might find something that will work at this website. Wall Mounted & Pressure Balance Shower Sets - Shower Heads, Rings, Rods, & Curtains | Vintagetub