The DT466 is a great engine.
So is the 3126, now know as a Cat C7 Acert IIRC.
The 3126 is a great motor, IF it is taken care of the way IT needs to be taken care of. I.e. it is a bit more picky than other engines. Almost all of the failures of the 3126 that I dug into were related to improper maintenance. The C7 has had quite a few updates, and is a VERY powerful motor. The downside of the CAT engines is there is almost NO aftermarket support for them, although CAT does make a high-output tune, something like 350HP and 1000TQ (yes it has that much torque). This is a newer tune available from CAT, so many people don't know about it.
If I was going to swap a CAT in I'd try for the C4.4 Acert. Same thing as the John Deere PowerTech 4.5L, the pre-PowerTech 4.5L (which itself is so similar to the PT) and Perkins 4.5L. It is a inline 4 cylinder turbo diesel, and is a reasonable weight.