Fork truck engines are RPM and power limited so that they last a long time and don't fail. For example, Toyota's current Tier IV 3.0L turbocharged 4-cylinder gasoline engine puts out a max 93hp at 2550rpm. They last a long time because they aren't making much power for their size, and they don't get turned very fast.
Still, that Toyota wouldn't necessarily be a good tractor engine. A Deere 5093E has the same 93hp Net, but it's 4.5L (and turbo-charged) at a similar 2,400rpm....50% larger to get the same net power. That's because it has to be to turn 2,400rpm for hours on end, and last for years on end.
You inadvertently confirmed what a lot of us have been saying all along- one can certainly make a gasoline engine engine "last a long time and [not] fail." The key is to keep the operating speed to a pretty reasonable level, which is why engine speed of industrial engines is much the same for both diesel and gasoline engines- 1500 to 3500 rpm, not the peak operating speed of 6000-8000 rpm of an automotive engine. The Toyota engine running at 2550 rpm will run for a very long time. That same engine rated to run at twice that speed would likely have a lifespan of a few hundred hours at full load at full speed but probably make 2.5-3x the power. That's why gasoline engines designed to run heavy constant loads are governed far slower than engines designed for lighter intermittent duty, such as in a passenger car. That speed is nearly always in the 1500-3500 rpm range. Even engines which can go faster typically are spending most of their time at that same speed. Look at your tach in your car when you are cruising- your engine is turning at 2000 rpm, not 6000 rpm.
Lol. Lol. Darkblack . . . you really neef to get coordinated with the other gas engine believers because you're telling conflicting stories. One guy tells us a gas engine 35 hp would be the same displacement as my Iseki. But then when I say that a 35 hp gas engine with equivalent cooling capacity would be more expensive to produce . .. then that conversation goes quiet. Now you're telling us another story.
That was me, and I took a brief moment to reply because my job has been very busy. The engine I mentioned is smaller displacement than your Iseki, 999 cc vs. ~1100 cc. It makes about as much torque but a lot more power. I can't find the price list for your Iseki, but the gasoline engine I mentioned is much less expensive in an otherwise identical finished product than a roughly comparable small diesel engine. Exmark uses the Kohler ECVs among many others in their ZTRs and they offer both the ECVs and Kubota's D902 three-cylinder diesel in the Lazer Z series top-of-the-line zero turn mowers. Exmark doesn't list the D902's horsepower but they run it up to 3850 rpm

; it makes 23.0 gross (not net) HP in the
BX2370 turning at 3200 rpm. The ECV980 (38 gross HP) in the Lazer Z with a 72" deck has an MSRP of a $16,205 while the D902-powered model has an MSRP of $19,757. The diesel-powered model is clearly and significantly more expensive, cooling and all.
Go out and invent the gas engine for a scut . . because nobody has seen one . . Until then you've got nothing but guesses and weak assumptions.
The reason why this hasn't been done was mentioned previously- there likely would not be enough of a marginal increase in total dollar sales to justify the engineering, qualification, and carrying costs of the additional model. There likely aren't too many people that would refuse to buy a diesel CUT/SCUT and would only buy a gasoline CUT/SCUT; the ones that would prefer a gasoline-powered unit would still be willing to buy a diesel-powered unit and currently do so. The gasoline-powered CUT/SCUT sales thus would thus really only subtract from diesel model sales and with their lower average selling prices, cause total sales figures to drop. So you have lower sales numbers AND higher engineering, qualification, and carrying costs for the second model line. Quite a payoff indeed. That is why you don't see them. That says absolutely nothing about the merits of the technology or equipment, only about the current market economics.
Trying to start your own company to make ANY new tractor would be suicide as well, also due to the current economy. The market is also very saturated with a bunch of different manufacturers in the game. Trying to be a tiny upstart competing with giant competitors like Deere/Yanmar, LG (LS -> CaseIH/New Holland's CUT maker), AGCO, Kubota, Mahindra, and others would be a huge challenge even if you had a superior product. It would be billions upfront before you can even think about seeing a dime in returns. Inertia wins out over innovation every time; just look at any other market sector.
The term we need is tractability. ... Analogous to area under the horsepower curve. Thats where diesels shine ... other than being able to work at their peak longer than a gas engine.
I think you are really trying to say that the flatness of the torque curve is really what we are looking for. A peaky engine with no torque until high speeds is not very tractable; one with a lot of torque from down low in the RPM range is very tractable. The torque curve is affected by a bunch of factors such as compression ratio, cam profile and timing, injection timing, bore vs. stroke ratio, intended operating speed range, the particular setup of your forced induction (if present), etc. etc. You can certainly make a gasoline engine with an extremely flat torque curve which would be better than a similar-sized diesel's. Just look at a modern undersquare multiple-small-diameter-turbo DI gasoline engine. Torque curves are essentially a straight line on them from not much above idle on through redline due to how the turbos are set up.