I just pulled the valves on my 23 and the stems
measure .308 and the head is larger diameter than
a standard "T" valve. Any idea what I have and
what I can do now? The guides are just a little loose, not standard .312.
Often larger than standard valves are installed to regain a good seat. I don't know about the undersize stems.
I use Fordson tractor valves which have a 1.66" head and are available in either 5/16" or 11/32" stem sizes. That way you can easily account for worn valve guides or bad seats without having to spend a lot of time and money. It is a lot less money and a lot less work than replacing the guide, seat and the valve. You will have to cut the Fordson valves to length and drill the retainer pin holes.
Valve guides have been sleeved maybe because someone wanted a large diameter valve head thinking they would get better flow and that is the size they found. Not a big deal or a problem. If it runs well, drive it, have fun.
The head diameter on the old valves is 1.499 and the new valves it is 1.467. The stem on the old valves are .308 and the stem on the new is .310
The stem will work but will the head work because the new valve is .032 smaller?
If the guides are reamed to .312" then the .310" stem diameter is perfect. The diameter of the valve head is fine so long as the valves are about 1/2 way "proud" of the cylinder deck.
As Mike said, somebody has likely installed guide liners. Take a close look before you plunge a reamer through it because it's possible they had to ream the original guide beyond 0.312 to accommodate the liner, in which case you'll have to use an oversized stem or install another liner to get it back down to the stem diameter that you want.