Details on intake manifold for Lesabre 2004, 3.8L

[oyama]

I'm going to replace intake manifold gaskets, both lower an upper (lower is leaking, can see coolant around).
My questions are concerning the procedure for changing the oil etc. Shall I drain the oil before the job and fill up after everything is place? I don't get why people recommend sometimes to take out the spark plugs - is it really needed?
I can find info about how to replace the gaskets but not so much about oil, coolant exchange, but that's equally important cause I don't wanna mess around with the engine.
Thanks!

 

[DonP]

It offers good time to assess the condition of the plugs and change them if needed.
I would drain the oil after, that way it can carry out any stuff that finds its way into the crankcase before you start the engine again, and do another change shortly after you get the engien running again. Since you will be draining the coolant when you start the job you will be replacing it anyway. A decent time to rinse out flush the system.