[Marky Dissod]

What kind of additives and chemicals would you run in the gas and oil?

Generally, I trust stuff from lubegard.com.
LubeGard has lots of good stuff.

Is it even something to be concerned about?

If you change the oil often enough, and use Chevron with TechRon Fuel System Cleaner, or anything approved by bobistheoilgy.com, you really don't NEED to use additives regularly.
However, whenever I get a new used vehicle in the family, I'll use
Bio/Tech Engine Oil Protectant - Lubegard in the motor oil with Group IV fully synthetic 0W30 ONLY
in cast the previous owner Toyoduhr'd the maintenance.

The rest of the ISSF will surely have plenty of good advice about how to prep the inlet manifold for re-installation, what sealants work best, etc.

 

[Marky Dissod]

All too often overlooked about the LT1 inlet manifold:
There is an entirely separate Idle Air Control inlet manifold hiding in plain sight, running parallel underneath the larger more blatantly obvious passages. (I call it the 'idlespider'.)
When the throttle is (completely) shut, the IAC motor feeds air to these slender paths.

Many LT1 inlet manifolds otherwise thoroughly cleaned, still had over 2 decades of gunk hidden in the idlespider.
For best results, remove that underplate, and don't forget about the EGR and PCV passages as well.

 

[Marky Dissod]

@sherlock9c1 did something before reinstalling the inlet manifold
... something to keep the inlet manifold cooler ...
a barrier? ... a coating ... can't remember ...

 

[Marky Dissod]

First I've heard of this "idle spider", but I'm not an engine builder or guru ...

Even fewer have seen it / noticed it, including many who have removed / reinstalled the inlet manifold.
Close up the front main throttle passages.
Blow smoke through the IAC passages (the spider's head).
The smoke will exit through the spider's legs.

 

[Marky Dissod]

Late to the party - @Marky Dissod I didn't paint anything.
Just keep that oil splash shield in place on the bottom.

ever taken a look inside your intake? ... one trick I used to make the car more consistent at the track was to coat the inside of the intake with a high temp epoxy ... trying to mimic the plastic LS intake to reduce the intake temps ... sprayed 4 or 5 cans of brake cleaner on the inside ... trying to get all the oil off before ... the epoxy would stick ...

... epoxy worked like a charm. knocked about 2 tenths off my ET compared to before ...
more importantly, it made the car more consistent and less sensitive to heat soak when I was waiting in the lanes ...

Apologies to both shrlock9c1, and stonebreaker.

Point is, while you have it off, no need settle for status quo - maintenance is usually a PERFECT time to upgrade.