[kipps]

There's two things to keep in mind.

#1, it's not worth rebuilding a generic 5.3 engine. The purchase price is too low to be worth the bother.

#2, most of the work of a swap is in the engine support systems; intake plumbing, fuel supply, cooling modifications, wiring, tuning, etc. Very little of the work is related to actually setting the long block in place.

Put those two things together, and yes, you might as well just replace the rear crank seal, oil pan gasket, and just stab it in. If it gives up the ghost in a couple of years, it should be a quick day's work to pull it out, and swap it for an identical engine. As long as the replacement engine is the same generation(24x vs 58x reluctor ring), the same displacement, and the same intake port style, it should be easy. No additional tuning or mods will be required to switch the long block.