A lot depends on your workspace, tooling, capabilities and the true scope of work you will embark on. Once the engine is out all work is indeed easier but pulling the engine is a relevant amount of work.
If you really are just doing the HG and hoses/vac lines and you either don't have the facilities or don't need to do more "while in there" I'd just do the HG in the engine bay, personally. I did the HG, coolant hoses, vac lines and quite a bit else with the engine in the 80 and would do it the same way again for that level of work. A piece of wood to use as a bridge makes it easier to get into the rear areas. Cutting the intake manifold so that it can be removed with the harness in place saves effort and minimizes flexing of the harness.