Something to consider on the plugs is the Autolite'* have the end cap built in and the NGK'* frequently are screw on ends. This means the part where the wire hooks can be loose and should be tightened before installation. Some have seen KR from these loosening.
Fllush before gaskets. Coolant flush takes me half to a full hour. Pull the draincock, open the radiator cap and let it all drain. Then flush into the rad cap area, overflow, pull the heater hoses..and upper radiator hose at the tstat housing. Flush it every way possible. Then fill or keep the supply going with the hoses hooked back up and start the car and flush while it'* circulating. After a minute or two.. turn the car off and flush every which way again. Repeat until you see absolutly no color for quite a while. Either Prestone LL or Anycolor.. to replace.
Leave the needle bearings on the SC. With your current mileage they should be fine for some time.
SC oil .. yes.. pump it out with an old spray bottle or a syringe/turkey baster (not the one you plan to use for T'Day) and refill with 2 bottles of oil or to the bottom of the threads at the plug hole.
Saw that you plan a coupler. You should still remove the oil ahead of time as it would make a mess on the engine. Ensure you get the GM red gasket maker. Small tube is all you will need.
On the valve cover gaskets..get the grommets as well. (Usually sold seperately).
for all o rings. Both fuel and coolant elbow. Lube them with lightly vasoline or grease to ensure reassembly goes smoothly. Not lubricating them could lead to a nick or pinched ring.
Another side note: If the engine is slightly dirty.. clean it super well before starting. This will help ensure that none of this muck gets into the engine as you take pieces off. And don't try to clean the inlet of the SC or any part of it beyond the gasket surfaces. (See my rotor coating peeling thread