7040, 7045 driveline strength

I had two 3116 Caterpillar engines in medium duty trucks, (rollback/winching) service. Both were worked hard, and required cylinder heads from cracking. Both were set close to 250hp. Don't know about the tractor, but I see a lot of the 7000 series with broken transmissions in one form or another at factory settings in farm service.

You are asking about durability of a 50 year old tractor?  Anything can break anywhere anytime. Having said that - the 7000 was one of  if not the heaviest built per HP tractor. We sold and serviced hundreds and can still count the few failures - most due to lack of maintenance. The first 7030-50's had an issue that showed up on the 4or 5 speed - and the drop boxes could have issues at high hours. That's it. The issue is they are so heavy. You got to have some kind of special class to allow a heavy tractor with an engine transplant.  As to farming with it - the weakest part would be the nut behind the steering wheel :-)  All units went thru beak down testing at 10% over rated power. 

If this wild hair ever does get pulled it will mostly be a farm tractor that is over powered for it's job. The only time full power will get used is probably discing in front of a field fire. It will run down the track once a year at a local farm tractor pull that I'd say has some pretty lenient rules. The reason I ask this in the pulling forum is this is where the most knowledge of stuff breaking probably originates

I know where there are a couple that pull 12 MPH "farm stock" classes and are at 500 to 600 HP and have done nothing to the standard transmission for "beefing it up".  You know that all the Farmall's have an additional after-market center bearing on their countershaft in the transmission, right ??

Will a 7040 with only two side gears in the diff be usable or would only a 7045/7060 differential be useable? If a 7040 diff would work I would be happy as I already have 2 7040's with bad engines. One PS and the other PD. Would it be a good idea to add a brass bearing shaft like on a semi axle behind the ring gear to prevent ring gear flex at the pinion? IDK what the technical term is for that...