old-boston—
Your stamp is definitely from plate 1 Late state, but it is difficult to pin down the exact plate position. It is a “B” relief, but doesn’t appear to have the customary guide dot at lower right. That’s hard to see however because the cancel falls across that area. If it doesn’t have a guide dot then that narrows the search down, because few B relief stamps lack the guide dot at lower right.
My best guess would have been that your stamp is position 30L1L, based partly on the appearance of the bottom of the stamp which we can see above it. But known copies of 30L1L do not correspond to your stamp exactly.
Billsey, are you out there lurking? Perhaps you have some ideas on this.
Below, my copy of position 20L1.
Can't help much, I haven't tried plating the 1851 one cent. Other than saying it's a #9. 🙂 I like the cancel, Boston / October 14th / Paid is how I read it. Someone sure didn't want to spring for the good paper...
