The Mosquito FB.VI Series 2 could carry 2 500lb bombs internally.
References:
Bombers of World War II, page 122:
"FB.VI: fighter-bomber, Merlin 21, 23 or 25, F.II guns plus two 227-kg (500-lb) bombs internal plus drop tanks/bombs/rockets (total 2,248)"
The Great Book of World War II Airplanes, Mosquito section by Bill Sweetman, page 361:
"The F.IIs and converted NF.IIs were, however, to be joined by a version rather better adapted to the Intruder mission. In late 1941 it was envisaged that the existing Mosquito II day and night fighters would be replaced by a heavier version with provision for bombs or fuel tanks under the outer wing. The F.VIA was to be a night fighter and the F.VIB a specialized fighter-bomber, with room for internal bombs aft of the cannon bay. With the advent of more advanced night fighters, the F.VIA was dropped and the intruder renamed FB.VI. Originally, two 250 lb (113 kg) bombs were to be carried, but the internal weapon load was doubled when the short-finned 500 lb (227 kg) bomb specially developed for the Mosquito was approved. Most of the FB.VI versions were equipped to take two of the heavier bombs internally plus another pair on the wing pylons - a 2,000 lb total load, in addition to the four cannons and quartet of machine guns."
Jane's Fighting Aircraft of World War II, page 115:
"Mosquito F.B. Mk. VI. Rolls-Royce Merlin 21, 23 or 25 engines. Developed from the Mk. II as a Fighter-Bomber with the standard fighter armament and accomodation for two 500 lb. bombs in the rear half of the bomb-bay, the front half being taken up by the cannon breeches. Provision for two 50 gallon drop tanks or 2 500 lb. bombs under the wings. Total bomb load 2,000 lbs. In action in Europe early in 1943 and in Burma late in 1943. Provision was made in 1944 for carrying four rocket projectiles under each wing in place of tanks or wing bombs. Emplyed thus by Coastal Command, mainly against shipping, ect. Length 41 ft. 2 in. (12.55 m.)."
Mosquito Bomber/Fighter-Bomber Units 1942-45 by Martin Bowman, page 54:
"The Mosquito FB VI boasted the same armament as the fighter version, but had the additional capability of being able to carry two 500-lb bombs in the rear half of the bomb-bay..."
It is mentioned in other places in books that I have as well.
