The bore marks indicate 3 provings:
1. 13/1 = .719 - .728" 1925 - 1954
2. .729 1954 - 1989
3. 18.7 = .736"post-1989
At the lower L is the London Proof date
It still has 2 1/2" / 65 mm chambers

The post-1989 proof would be to the higher CIP pressures, but 3 TONS was for a max. service pressure of about 9,000 psi. It passed CIP proof, but the wall thicknesses should be carefully measured

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