A few additional points about seam filling. Make a point at getting to where you are comfortable with restoring surface detail as this will lower the stress level somewhat with seams and sanding. You can also tape on both sides of a seam to reduce damage from sanding.

Black CA glue applied surgically with a stiff wire works well for me for seams. It does not shrink and can mostly be scribed the same as plastic (as long as you use a light touch to avoid digging into the glue). It can be very quickly set using accelerator or you can wait about 30 minutes (sometimes less). The key is to put on small amounts and thin layers, then work these down with skinny sanding sticks. I almost never sand with anything heavier than 400 grit. If I need to reduce something before finer sanding, I will use a jeweler's file with light strokes, cleaning the file regularly with a small wire brush. Sanding sticks can be cleaned using either a piece of denim or a pencil eraser.

Try to avoid damaging surface detail, but if you do (and you will no matter how careful you are), having the ability to restore that detail using tape, straight edges (especially if you can get a flexible one) scribing tools, razor saws, small drills, knife edges, or micro punches (used for leather embossing) will usually get you back to an acceptable point.

Dear all @fiveten, @johnb, @clipper, @lis and @stephen-w-towle, thank you all for your advice! I had some time available today and really took my time with sanding. It’s interesting to see how everyone has a different approach. I have never used CA glue for this. Like John, i use acrylic putty. I really like the one from Vallejo. Slowly getting there!

1 attached image. Click to enlarge.

Great job, my friend @fxrob!

Nice progress, Felix @fxrob. The Vallejo acrylic putty is indeed also the one I use. It does the job quite nice in most cases.

These two liberators fit perfectly into the airfix kit. Interestingly, the manufacturer of the decal (unfortunately unavailable today) does not distinguish the shape of the bombardier window depending on the manufacturer.I Try to find red letters. If it will be possible - this interesting RAF painting could be done by myself.

1 attached image. Click to enlarge.

@fxrob Yes this 223 squadron liberator is realy Ugly. I Like this "Night" scheme BL@V or X. I think It is possible to make this painting with aftermarket decals (number and letters).

Gentlemen, you have noticed that we missed an important detail of the Airfix model. Armor plates on both sides of the cabin! See in the photos, not all planes have them, like on Airfix sprues! I'm not even sure the Vailant Lady Model has this detail. From my decal sets Naughty Nan and Miss Judy seem to have it.

The armor is not too difficult to add. You can either use very thin styrene or heavy duty foil depending upon the desired final results. The main thing to remember with thin styrene, however, is to be careful how much cement you put under it because it is very easy to distort the thin plastic.