Anything can fit with enough money and modification. Although a delete kit which includes new turbo back exhaust, tuner, and EGR delete will cost around $1,700 which will end up paying for itself in the fuel economy increase in about 50-75k miles depending on fuel prices.
If the CP4 of the new Cummins is a concern, a few places already has CP3 conversions the 2019+ Cummins for about $2,500 which you can get some of that back by selling your CP4 back to them. Both of these would likely be cheaper than and less time consuming than replacing the engine with an old one.
The cumminsforum.com or turbodieselregister.com are probably better places if you want more specific information on Cummins diesels and mods. However, modifications are more welcomed on cumminsforum than they are at turbodieselregister or here so that is the place to go if you want to talk mods.