No mention of fuselage changes between the Manchester and Lancaster prototype. Except for the eventual deletion of the centre fin (which happened on poduction Manchesters anyway).
Yes indeed; the first prototype Lancaster was a bog standard Manchester, but was to be the first Manchester Mk.III as it was originally intended, serial BT308, modified from the Manchester production line. Apart from a larger wing and four Merlin XXs, the aircraft differed in a few key areas. Armament wise, the top turret was changed from the unpopular Nash & Thomson FN.7 turret to an FN.50 turret and the nose and tail turrets remained the same, the nose was an FN.5 and tail an FN.20 in both aircraft, with the exception of the first few Manchester Mk.Is, which had the FN.4 tail turret. Manchesters also had FN.21 mid under turrets, which were removed in production examples, but the Lancaster was not fitted with this turret.
On BT308, the three vertical fins of the Manchester remained, but this was changed to two taller fins and the deletion of the centre fin. Interestingly, this was done on BT308 before the taller fins were added to Manchesters on the production line, which occured in July 1941, so Lancasters being built had them before Manchesters. To put this into perspective, the Manchester Mk.III, which was renamed 'Lancaster' was ordered before the Manchester entered RAF service in November 1940. It was always intended on being a four-engined aircraft and Roy Chadwick had begun feasibility studies into a four-engined Manchester in 1937, whilst the final configuration of the Vulture engined Manchester was being undertaken.
On (? exactly when I'm not sure) Lancaster Mk.Is, the bomb aimer's nose cupola was enlarged, which might account for the extra inches added to the length of the Lancaster over the Manchester. The Lanc also received new main undercarriage units that could fit the Halifax main wheel, and a new tail wheel leg. Crew positions remained largely the same, with the exception of the deletion of a second pilot and the addition of a dedicated flight engineer in the Lancaster - see the previous post for further info on crew changes. The bomb aimer was a Wopag, the front gunner (obviously).
The aerodynamic and stability issues that affected the Manchester did not affect the Lancaster as most had been cured or lessened with modification, including the vibration felt when the tail turret was turned was cured with the addition of an aerodynamic fairing in front of the turret, the elevators and horizontal stabilisers were lengthened to cure further instability on the Manchester and the disrupted airflow from the actuation of the FN.7 mid upper turret as it hit the centre fin did not affect the Lancaster owing to the absense of both, although a fairing was added around the Lanc's mid upper turret to address turret rotation issues.
In short, the Lancaster most certainly benefitted from the development of the Manchester, which was troublesome, but had potential. It was underpowered and this was cured with the addition of two more engines. System wise, the Manchester and subsequently the Lancaster was an advanced design for the late 30s, with most systems initiated electrically, with a complex hydraulic system operating the flaps and undercarriage. The Manchester did have electrical reliability issues in service, but these did not translate over to the Lancaster.