Hello John, it’s possible this was/is a commercially available typeface, but it also might be an old concrete stamping letter set made exclusively for that purpose and was never digitized.
I’ve not seen a font that shares all of the characteristics of the lettering on the memorial in your photo, but if you just need something close I would do a search for “typewriter fonts” or “slab serif fonts”.
If the client would like to match it exactly it will need to be done manually, feel free to use the MLC matching service: https://www.monumentletteringcenter.com/product/cemetery-inscription-matching-service/