I have been using the base of the T series as you might’ve been able to get from the name because I think that that would be the most realistic vehicle that gavril would base it off of
the main issue being that lorries and tractors are built entirely differently and it would be better to start from scratch, tractors don't have a frame per se, the engine and rear axle housing are the frame. Not to mention the difference in operation with regards to gearboxes, lack of suspension in the same capacity as a road-focused vehicle, and them being designed for entirely different purposes.
its not the most realistic as alex farmer and bussin buses said but it seems like it could be a good addition to the game but if your basing it off of the t-series frame i would reccomend the shortest possible frame combination instead of the current one and making the hood and cab smaller and the rear wheels should be significantly taller than they are