Looking at the proof marks I see :-
A Proofed under 1954 Rules of Proof vis .729" 2&1/2" 3 tons.
This would align with LP76 indicating re barreled in 1976
B.Sometime after 1989(introduction of Metric marks) chamber was lengthened to 70mm (2&3/4") . At that time it would accept a plug Gage of 18,6mm but no larger, bore dia so marked.
C.There appears to be a second LP date stamp that I cannot see clearly. this probably reflects the re-proof of Item B.
D There is nothing in the marks to indicate a light honing.
The .729" stamp merely confirm that a plug Gage of .739" would not enter the bore to a depth of 9". A dia of .732"/18,6mm would have been marked as .729"
Hope this helps, any other interpretation welcome,pls confirm if ther is a second LP mark and what date it reflects
