The choice of A-Model to reproduce the first prototype, instead of the more publicized second prototype TsKB-19 or the third prototype TsKB-19 bis, is probably due to the availability of good drawings of the first one only (at least, to the date of the kit release).
 

If we want to convert the A-Model kit into the TsKB-19, we have to: extend the rudder at its lower section; modifying the nose profile (that should be more protruding on its upper part, and slightly different on its lower part, just behind the spinner junction; remove the oil radiator cowling; adding the supercharger inlet under the fuselage; replace the spinner with a longer one, with starter tooth protruding;

	fill the old undercarriage bays and open new ones on the piece B3; deeply modify, or scratchbuild, the undercarriage legs, doors and bays; note that the main undercarriage has fork legs and pneumatically actioned struts, and has't the retracting wire as on the first one; scratchbuild the underwing water radiators (both in semi-retracted or fully extended position);
	modify the panels of the wing/fuselage joints; shorten the ailerons and engrave the flaps; omit the small circular windows on the nose, in front of the windshield.

This is the color scheme used for the Paris and Milan exhibitions in 1936/37: overall gloss white (it looks white as on most Polikarpov prototypes, but some people identify it as light blue grey or silver); polished metal engine cowling, extending to the wingroot front panels too; natural metal prop blades, with partially black or dark blue rear surface; with gloss red tail, with a very soft demarcation line; the guns are removed or simply not protruding; the pitot probe looks red.

drawings adapted from Letectvi Kosmonautika

 

TsKB-19 bis

 

The third prototype TsKB-19 bis is known in two configurations: the first configuration differs from TsKB-19 for: new two-piece, rearward-sliding canopy with well visible external guides; it looks slightly higher than the older type; 20 mm gun and starter tooth protruding from the spinner; outer wing guns deleted (only two ShKAS were retained); underwing cooler fairing slightly extended rearwards; it looks painted red with polished alluminium engine cowling.

The later configuration features the same characteristics, plus: modified and partially removed main undercarriage doors; additional cooler under the nose, in an asymmetrical position to not cover the supercharger intake; dark repainted (black?) engine cowling.

This drawing resumes the differences between TsKB-19bis (late configuration ) and TsKB-19. The drawings are shown on the screen with a standard resolution.  When printed using a 120 dpi resolution by a photo-retouch or graphics program, they are in 1/72 scale.

The drawings are an adaptation of existing ones to demonstrate the differences between  the two prototypes.
Being not particularly good drawings of the undersurface of the second prototype, some lines are approximate. The drawings are shown on the screen with a standard resolution.
When printed using a 120 dpi resolution by a photo-retouch or graphics program, they are in 1/72 scale.
There are uncertainties on the overall lenght of TsKB-19: taking a TsKB-15 profile as a base (7400 mm long) and leghtening its spinner, the resulting lenght is about 7560 mm (reported on some sources), while Aviacia n.12 reports 7365 mm for TsKB-19 and 7420 mm for TsKB-19bis (differing only for the starter tooth); if this is true, the fuselage of the TsKB-19/19bis should be shortened of about 140 mm, but it is not clear where this should be.
The drawings reported on Aviacia, despite their merits in describing many characteristics better than in the past sources, aren't coherent with this data.
I would suggest to ignore this discrepancy, in consideration that the Amodel kit is already too short of 2 mm.
 

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technical details	Building the Amodel Kit	converting into TsKB-19	Photos of built models	VVS Modelling Main Page