There is a long debate about using the booster line and the seafoam not being distributed equally to all cylinders as well as equally throughout the intake, etc... since it is so far to the back and directly across from an intake runner...
Best place I have found on the 4.0L OHV is designated by the big red arrow in your original pic below... it's a little tight getting in there, but worth the effort once you see just how perfect this location is for seafoam treatments...
Just remove the line there, being careful to not break the plastic clip, and attach any old rubber vacuum line long enough for your needs, make sure to plug the line you remove with a bolt or rubber plug and place it out of the way of anything it could get caught on when the engine is started. Then just idle the engine and add in whatever amount of seafoam you require. The vacuum from this port will suck up the seafoam quick, so be careful. have someone to help you with keeping the idle up to about 1000 rpm's and all should be fine. Using this location will undoubtedly reach all of the intake and cylinders equally, as it is brought in through the throttle body. I've been doing it like this since I first owned my truck, and i never had a problem. Once your done, just pop on the line and clip you removed, and your done.
