AMF, there are no serial numbers on the actual valve in the wall??

if you can remove the cover, take a pic of the valve, call Delta, maybe they can advise you.

try this.

https://allthumbsdiy.com/plumbing/how-to-identify-a-faucet-brand

Teeth (spline) count

In older houses, it is common that you can’t find an identifying brand logo, name or model number on the faucet itself. In this case, you will need to remove the broken part.

You most likely will be able to obtain the correct replacements parts by first removing the faucet stem and count the number of splines on its broach. Also, measure the length of the stem from top to bottom.

The broach is atop the faucet stem, resembling a shape of a small-toothed gear. The purpose of the gear’s splines is to fit inside the female end of a faucet handle to control the opening and closing of faucet valve.

• 4 point square broach – Milwaukee, Royal Brass, Speakman, Sterling, American standard, Chicago, Concinnity, Gerber, Price Pfister, Symmons, Zurn
• 8 point broach – Briggs
• 12 point .335″ broach – Crane Dialeze, Michigan Brass, Wolverine.
• 12 point .375″ broach – Arrowhead, Artistic Brass, Harcraft, Glauber, Price Pfister, Scoville, Universal Brass.
• 12 point .39″ broach – Bradley, Elkay, Fisher, Sears, Universal Rundle.
• 12 point .415″ broach – Symmons.
• 12 point .485″ broach – Crane, Symmons.
• 15 point broach – Santec, Savoy, Wolverine.
• 16 point .360″ broach – Gerber, Sayco.
• 16 point .370″ broach – Acme, American Standard Cadet & Colony, Barnes, Burlington, Central Brass, Concinnity, Eljer, Glauber, Harden, Kohler Trand, Milwaukee, Newport, Phylrich, Royal Brass, Scoville.
• 16 point .40″ broach – Sterling.
• 17 point broach – American Brass, Mansfield, Midcor, Phoenix, Streamway.
• 18 point broach – Briggs, Indiana Brass, Union Brass.
• 20 point .285″ broach – Broadway, Concinnity, Danfoss, Dornbracht, Eljer, Grohe, Jado, Kohler, Milwaukee, Paul.
• 20 point .415″ broach – Broadway, Speakman, T & S Brass.
• 22 point .375″ broach – American Standard old 3/8″.
• 22 point .438″ broach – American Standard current 7/16″.
• 38 point broach – Import, Pegasus, Glacier Bay.
• D Broach – Delta, Milwaukee, Universal Rundle, Valley.
• Oval Broach – Delta, Moen, Mixet.

some others,

you can send them a pic

https://www.guillens.com

another link

https://www.hunker.com/13416398/how-to-determine-the-shower-faucet-type