So I’m helping a guy get a case 85xt running after his brother died and left it taken apart. Crank shaft rods pistons and who knows what else is missing. I here the engine is basicly a Cummins 4b but with a few variations. Can I swap a Cummins 4b in and swap over accessory’s etc?
yep, Case actually developed that engine series (3.9 and 5.9 liter) and licensed it to Cummins to manufacture.
Do you know what parts are shared vs what’s different? Can I buy a 4b and drop it right in?
Yes
You can drop in a either a 4B or a 4BT but a 4B is naturally aspirated and will have significantly less horse power.
The 85XT was naturally aspirated & rated at 69HP. If you bought another engine & it was lower or higher horsepower - you could fit the original injector pump to the newer engine, as that is what controls the HP. Get the numbers off the injector pump & ask a diesel fuel injection shop to tell you the HP rating of the engine. I wouldn't fit a turbo model as there would be some differences in intake & exhaust that would need modifying & add to the cost. Would all the missing parts be at a local engine machine shop?