Anyhoo.. came across a brand new unfired 22/45 5.5" upper with box and rail. Thanks to the valuable info I could locate here and other forums, after ~2 hours of careful filing / sanding.. and removing the nuisance LCI, the 22/45 is now tighty-tight fit on my SS frame..
Range time will be tomorrow at the earliest, will update result. Below are pix on before and after.
BEFORE:


AFTER:


