[Flatsole]

You want to spray it into your intake manifold, which is the lower center of your pic.

 

[Flatsole]

That might work, it's pretty small though. The vacuum line you originally circled off the brake booster should logically go to the intake manifold but I don't know if it's a straight shot or branches off places where you don't want the chemical.

I'm pretty sure some guys have pumped it in upstream of the throttle valve at that purge line connection on the intake hose.

 

[Flatsole]

I disconnect the smaller hose and valve here and spray into fat intake hose. BLUE CIRCLE View attachment 141784

That's what I would do.