Scania 420 vs 360

You do know Scania has stopped making parts for the 3 series?

 

I wish people will stop thinking maintaince lower.

One good set of potholes leave us replacing two tires once in a while where we live just after each winter.

 

Good morning.

Had a look at Scania website, see they have two 14 speeds, one is overdrive, the other is direct drive with a 16.5 crawler gear. (I think)
The direct drive would be better for your needs due to it's lower crawler gear, but with the small engine I fear it still might be too fast.

For comparison:
Typically, here in Canada, we can haul 140,000 lbs with super B trailers.
You will see engines with 500 hp and 1850 ft/lb of torque or greater, with 3:90, 4:10 or 4:30 gears and an 18 speed transmission with 2 overdrive gears and a 14.4 crawler gear, they tend to have a target cruise speed of 90 to 105 km/h at 1500 rpm or higher.

 

I think you're pretty close in your thinking.
Definitely a direct drive transmission with the deep bottom gear and deeper than a 3:42 rear ratio would be to your advantage.

If you could find the power curves for those engines and manufacturer's driving recommendations it would make it much easier.

I'm not familiar with the Euro trucks, but I imagine instruction would be similar to engines in the NA market.
When hauling loads over 90,000 lbs they recommend using the high end of the power band, cruise at or near 1500 rpm to reduce stress on the engine and keep it in the sweet spot all the time.
With big weight, the bottom end of your engine gets hammered a lot harder if your rpm's get too low, best to stay away from low rpms unless you are loaded light or empty.