Sorry Hank, I do not have the model and spec numbers as requested, I cannot find the owner's handbook. My best guess is that it is a single cylinder Kohler engine, side valve, approx 1990 vintage, and the mower is labelled 12.5 hp electric start.
In order to get the model number I will have to carry out major reorganization in my garage, since my mower is buried under other household objects. This will lead to a delay of about a day before I can answer you.
I have at last unearthed the mower, and find that engine details are as follows:
KOHLER COMMAND 12.5
Model CU1258T, could be CV1258T
Serial No. XXXXXXXXXX /p>
Thank you Hank for the information. I have so far been unsuccessful in ordering the valves through the internet, but will try by telephone in due course