Does some of this sound familiar?? (See post #2.)
From this link describing an attack on Chiba (which is near Tokyo, 100s of miles from Sapporo) on July 6, 1945:
https://military-history.fandom.com/...n_World_War_II
Air Raid of July 6, 1945
On the night of July 6, 1945, 129 B-29 Superfortress from the USAAF 58th Bombardment Wing departed from Saipan. Five aircraft were forced back, but the remaining 124 aircraft arrived over Chiba at 0139 hours and
commenced a firebombing attack with 889 tons of E-46 500 lbs incendiary cluster bombs and 500 lbs T4E4 fragmentation cluster bombs on the central part of the city from an altitude of 9900 to 11,500 feet, lasting until 0305 hours.[4] The E46 incendiary bombs were set to open at 5000 feet, releasing incendiary devices on the largely wooden city. The resultant firestorm destroyed 43.5% of the city. The estimated civilian casualties in the July 6 raid was 1,204 killed. The B-29 bombers returned to the Mariana Islands without damage or loss, although 14 aircraft were forced to divert to Iwo Jima due to mechanical problems.
889 tons divided by 124 planes come out to a little over 7 tons of bombs per plane. (See post #5.) Note the maximum bomb load of a B-29 was 10 tons and the maximum was not carried on long distance raids.
I think this Chiba report was somehow garbled or copied in part and became part of the description of the "supposed" B-29 Sapporo attack (post #2).
The casualties as given in post 2 may be the actual 2 day totals resulting from the navy attacks on all of Hokkaido.