I think you're both absolutely right. The original, brown one has minimal O of SOIT visible at the back of her truncation, but the redder one has the O near complete, so for me, yes, one is obverse 4 and one obverse 6. I suspect a rewrite of your half pennies page will be coming, Richard! So, two new discoveries rather than one! Whoever was on B repairing duty at the mint for these two dies was having a bad time!!
Any more of either obverse out there in forum land? Check your 1861's everyone!