Lip on the bore? You may need 2nd o/s (0.5mm) you dont often see lip on Hondas even over 100,000 mile ones
Turns out the lip was carbon deposits - bores showed signs of previous partial seizure & freeing off probably from years of storage - having +0.25 rebore.
I have removed the external gear shift mechanism so once I have prepped the various bolts ready for removal I will seperate the halves early next week - provided it stays warmish.
I'm going to make a small wooden support frame for holding the engine casing upside down to make seperation easier. (I am a hoarder of wooden offcuts.)