L series engines are tough little bastards. They can be quite noisy due to rattle chain noise.
I have seen an L18 in a ute so I know it's possible. I just don't know exactly what needs doing.
One thing that definitely needs to be modified is the engine cross member. the oil pan on the L series is the other way round. As for diffs, a 180B diff center is bigger than a Sunny diff center so caution may need to be applied.