As the title says, which version of the IL-8 have they modelled, as the vehicle present doesn’t represent any of the prototypes built? Looking at the model it seems they have used the model of the IL-8-1 which was equipped with a 12.7 mm (0.50 in) Berezin UBK machine gun on a VU-8 flexible mount. Otherwise the gun armament was identical to the older IL-2 aircraft with a pair of 23 mm (0.91 in) VYa cannon with a total 300 rounds and a pair of 7.62 mm (0.300 in) ShKAS machine guns with 1500 rounds in the wings. Optionally two 37 mm (1.5 in) Nudelman-Suranov NS-37s could be installed instead of the VYa-23 cannon. The rear fuselage was lengthened by 1.42 m (4 ft 8 in) to improve airflow and the landing gear was lengthened to accommodate the larger propeller.
This prototype with the VYa-23 cannons and a wooden rear fuselage was tested alongside a second prototype il-8-2 armed with NS-37 cannons installed and a metal rear fuselage. These prototypes were tested in may of 1943 as seen in the photos, but they lacked the capacity to carry 1000kg, instead limited to 800kg, prompting a third prototype also confusingly named the IL-8-2. This prototype had its armament again changed as the Nudelman-Suranov NS-23 cannons were replaced the YVa-23 guns and the UBK was upgraded with a 20 mm (0.79 in) Berezin B-20 cannon in a VU-9 mount. A cassette of ten AG-2 aerial grenades was fitted to enhance rear defense.The bombload was upgraded to a total of 1000 kg compared to the 800 kg (1,800 lb) of the first prototypes. The Il-8-2 made its first flight on 13 October 1944.
the third prototype was the one fitted with the 1000kg payload as advertised and doesn’t particularly look like the model presented, with the biggest different being the 4 prop propeller, and its appearance is closer to the il-10 currently in game
Photo of IL-8-1 clearly the model they have chosen for the plane in game:
I was also reading up on the IL-8 out of curiosity and as you mentioned there are signification differences between the prototype models (like used cannon weaponry etc). So far I understood it seems indeed only the 4-bladed IL-8-2 (being similar to the IL-10) or specifically the NS-37 variant of the 3-bladed IL-8 could carry the 1000kg maximum bombload.
Aye i need to get access to this book, * Gordon, Yefim; Komissarov, Dmitriy and Sergey (2004). OKB Ilyushin: A History of the Design Bureau and its Aircraft. London: Ian Allan. ISBN1-85780-187-3. but from my understanding the prototypes differ greatly, both in composite design, and armament.