Hello Mr Campbell -
You're right - for the Lancaster to handle such a payload was quite an achievement. Apparently, a lot of modification work was carried out : the nose and dorsal turrets with all their associated weapons, ammunition and equipment were 'ditched' and ammunition for the remaining tail turret was reduced by 20%. In addition, the outboard bomb-loading stations and related load-carrying beams in the wings ( which were hardly, if ever, used anyway ) were removed as were, of course, the bomb-bay doors and related equipment. The fuel system was also modified as fuel for the 'Grand Slam' raids was not normally carried in the outer wing tanks.
Even with that lot, I'd imagine take-off was 'interesting' - mind you, the return flight must have been fun !
