Oil consumption aside, a Diesel engine doesn't "burn" engine oil like a gasser. To a Diesel, oil is fuel. If it's going through combustion, it's getting burned. What you are seeing is either oil after combustion (in the exhaust) or cold combustion (retarded timing). Before considering a rebuild, find the problem. Start with a compression test. If it checks out, look into fixing the leak, such as valve stem seals (common, especially if N/A, with little/no exhaust manifold pressure). Install a pyrometer, and monitor the EGT before, during and after smokey periods. Check/advance the IP timing. Soot around the tailpipe is relatively normal. Oily bumper is more likely oil leaking UNDER the vehicle (rear main seal, etc.) and collecting there while driving at speed.

An engine R/R is a major undertaking for most people, and a van is much more. If you can't DIY, then consider replacing the van entirely. The cost of a store-bought (or shop rebuilt) long block will far exceed the value of the vehicle, and that doesn't consider labor and ancillary costs.