IRL, anything lean-of-peak is going to run hot except at very low power. A carbureted engine (read: not actively managed) will not last running lean, and that is a big important metric that is completely absent from the game.
One thing that fuel mixture absolutely CANNOT be in an automobile is a fixed number. 13:1 while idling fouls plugs and lets gasoline drip past the rings into the oil. Under power, 13:1 is on the lean side of reliable. Most carb'd engines had secondaries that ran rich of 12:1 to keep the temp under control.
Both rich and lean are problematic IRL for catalytic converters--high EGT from being lean or unburned fuel entering the cat both heat the thing up. The mounts for the ceramic catalyst fail, the catalyst rattles around in the housing for a while, then it shattters a little at a time and blows chunks out the tailpipe. Or it burns through the housing and falls out. Either way it's bad.
On engine weight--IRL it's not just the weight of the block for an OEM, the frame has to get heavier to stay in one piece. In-game, vehicles don't lose reliability from being overpowered to the point that a real frame would twist. But you are correct--swap block A and block B, the weight difference doesn't matter much IRL or in-game.
I wish the in-game fuel economy was less cryptic. The EPA test isn't much better--about 50mph is it for the EPA highway estimate. It gave the industry uniformity, but has not been altered since the repeal of the 55mph national speed limit. Automation might use a European standard for all I know. It produces poorer fuel economy numbers, but anybody who buys a car today usually finds the EPA Hwy estimate hard to beat. I can't drive 55, not even on my old Honda rebel. Maybe on a windjammer...