More great progress!

For the heat gun, I use this cheap one: https://www.harborfreight.com/1500-watt-11-amp-dual-temperature-heat-gun-56434.html

It is overkill even, as you dont need much heat, just something that can apply heat consistently, in order to add some pliability to the decals so that they can be better pressed into place with a cotton bud. I usually hold the heat gun about 8-12" (20-30cm) from the subject and only for a few seconds.
It is a delicate process, but the heat alone can help with certain decal type, much the same way that warm/hot water helps with decal applications.

I would recommend careful experimentation, and perhaps there are some youtube videos. It is too easy to apply too much heat, so be warned, you dont want to melt plastic, and certain carrier films can shrivel quickly. Also, I would advise against using heat while decal solutions are still active on the decals, or before the decals have set in place. Good luck if you try it, and hope it may be a useful tool for someone.

That's an interesting trick, my friend @pb_legend!

@pb_legend Andrew, thank you for the explanation! I definitely need somethings like this heat gun – will see what my local store has. I'm also thinking about using it for deformed plastic parts, when you need to bend it a bit or something. I use boiled water for resin parts, but that's too much for styrene.

@gblair Thank you, George! Things which don't fit are coming – I've started to work on the engine and here we go.

@johnb Thanks, John!

@fiveten Thank you, Spiros!

To close the fuselage, I need to assemble the part from step 4. I think it's the intake of a carburetor or something. For some reason it has a lot of detail, but the only thing you can see is the intake itself and that's it.

The tailwheel section needs a little pressure to fit into the fuselage. Just a small nuance.

Meanwhile, I've started assembling the engine. The kit suffers from a lot of flashes on the small parts. The three main pieces don't really go well together either.

The exhaust needs some work and drilling (I use a 0.45mm drill), but first of all you have to be careful not to remove the locating pins when cutting them out of the sprue.

And here we go with one of the legendary questions in the world of scale modelling - what colours should I paint the engine? The instructions say it all in aluminium colour. I did some research and my conclusion is that it should be an aluminium colour for the cylinders, blue-grey for the crankcase with black for the pushrods and a yellowish colour for the electrical wires.

Montex yes

Great work on the engine, Dmitry @starfar
A beautiful reference picture which confirms that your chosen colors are very plausible.

Those decals do behave verynicely, Dmitry @starfar
They follow the surface nicely.

Great decal job, my friend @starfar! Indeed, decals followed the surface texture nicely!