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Mark
Final paint scheme for HBII 42-97942.

Latest research from the facebook groups 379th and b17flyingfortress.de/en/ suggests HB II was part of Lockheed Vega built Block B-17G-40-VE: 42-97936 to 42-98035
Modifications to this production-block
Stowage positions for extra SCR-274N radio units added from 42-98015. Reduced number of supercharger fixing bolts. Ball turret disconnect switch added.

The previous block: B-17G-35-VE: 42-97836 to 42-97935 saw the addition of the staggered waist gun positions.
Camouflage paint finish was deleted during manufacture of Block B-17G-15-VE: 42-97436 to 42-97535

In March 1944 the first NMF B17's began to arrive on squadron. Orders regarding new tail insignia and aircraft codes were put on hold due to the build up to D Day. Eventually, Fuselage squadron letter codes (FR) were deleted and replaced by a single number (2) in the top of the yellow triangle surrounding the black triangle. The a/c letter code (K) was moved to the base of the triangle underneath the a/c serial number in the bottom of the yellow triangle. This was not completed until September due to lack of paint supplies.
Aircraft 42-97941 – the previous a/c off the line, is pictured wearing the black triangle with white Group ID (K for 379th) which it was supplied with. It has the "old" squadron fuselage letter codes (FR for 325th) and a/c ID code (K for HBII) under the tail triangle and serial number.
Note: Chin turret and fairing are grey (primer?)

The cover of the eBook The Last Flight of Heavenly Body II has a picture which I believe is accurate for the time of June 1944 for a B17G from Lockheed Vega of the correct block with correct codes and triangle for HBII.

Mark
The Fate of the Crew and of Heavenly Body II
42-97942: Delivered Denver 11/4/44; Kearney 4/5/44; Dow Fd 23/5/44; Assigned: 525BS/379BG [FR-K] Kimbolton 24/5/44; on return from mission to Enguine/Catts 19/6/44 Pilot: Lloyd Burns, Bombardier: Jack Gray, Engineer / Top Turret Gunner: Leon Gibbs, Radio Operator: Leroy Monk, Ball Turret Gunner: Bill Farmer, Waist Gunner: Dick Andrews (6RTD); Co-Pilot: Fred Kauffman, Navigator: Ed Sadler, Tail Gunner: Lou Schulte (3KIA); mid air collision w/44-6133, wreckage crashed Canvey point mud bank, River Thames estuary, UK. MACR 6983.