Old sparking plug cross-references

["Daren Stone, D2 Mfg. Engr. C5/6, 5-9521" <DSTONE@SC9.intel.com>]

     Okay, I'll be more specific:

          The handbook for my Riley ('48 RMA) specifies
     Champion L10S sparking plugs. Assuming this plug is no
     longer called this (or no longer made) can someone
     provide cross-references for either newer Champs or
     other brands ?

          Thanks in advance- 
                            Daren