Don't know how I missed this thread
https://doublegunshop.com/forums/ubbthreads.php?ubb=showflat&Number=355905

p. 4
"I currently own a 2" Churchill 'Imperial' SLE that was proofed at 1-1/8 oz. out of the London Proof House. Sold new in 1954 with the typical XXV 25" barrels and choked .015" and .017"."

That 1 1/8 oz. would be under the 1925 Rules. Post-1954 the proof would be in TONS and chamber length 50 mm