First, please do not take offense at any of what I say here--my intent is to help guide you in a direction that will allow you to get this task accomplished safely and at least cost. There is the risk that these priorities cannot coexist, IF your car has any damage (ie. bad knuckles) that isn't known at this point.
I am assuming some things about you based on the way you asked your original question and even your member number--yes, you've been profiled!!! Even if I'm wrong, this discussion may help someone else with the same or similar problems who read this later or has been reluctant to ask. No issue with asking questions here.
For the record, Moog is not in the business of helping GM sell parts. Also, Moog does not make knuckles.
I can't remember the exact wording, but I will have to assume that the context of the statement that has prompted your inquiry to the Forum (on a sheet of paper included with the ball joints) says "replace the knuckle" and has to do with checking the taper fit of the ball stud(s) on the part. IF it does not meet the criteria decscribed in the statement, then it IS necessary to replace the damaged part--in this case, the knuckle.
So, here's the scenario:
Question: does your car have damage to the tapered bore(s) on either knuckle?
Answer: you probably don't know yet, because you are still driving the car.
That may assume too much, so the next step in the process is to ask this series of questions--
What symptoms does your car have that are telling you to replace all of the front end wear components?
Is the car driveable?
Has it been diagnosed by a professional front end shop or other competent tech to determine that certain conditions exist that require part replacement?
My point is this--being that your car is a 94 model and now 10 years into its life, with possibly lots of miles, and guessing that you may not be the first owner, it may be a matter of knowing for certain that the parts are in fact worn out--there are some visual indicators--but if you're new to this task and lack experience, you need to do a little homework. There are a number of maintenance books, both from GM or from many parts stores, that will offer some help in the diagnosis. You are past that point possibly since you have made the decision to buy the Moog parts.
Your car may or may not have a knuckle problem. It is not possible to tell without starting the task of disassembling the front end. I understand that this car is very possibly your daily driver, and that you may only be able to afford to have it down for a weekend.
IF you begin the job and DO find damage to a knuckle, I'd say it depends on just how severe the problem is. If there is taper damage, I suggest that you either put the car "down" until you can get a replacement part, or if you MUST drive it, put it back together and drive it as little as possible until you gather up the rest of what is needed.
Unless you find damage that is so bad that failure is imminent, do not put new ball joints into use if you KNOW there is taper damage to the knuckle--it will only lead to rapid damage to the new parts, and you will have to buy them (ball joints) again to install with replacement knuckles.
Unless something has happened over the past 10 years to the ball studs on the car now, they stand a good chance of being OK as far as the taper fits in the knuckle(s). Alot will probably depend on the condition of the car. Being that you are in Illinois (where is Palos Heights?) you may find corrosion is an issue with the tapered fits after this long--or it may be just fine. Just another thing to consider in the process.
Other things can happen to the knuckles--spindle pin damage from bearing failure, bending of steering arm from a collision, too much wear on the caliper contact points, etc.
You can find useable replacement (used) knuckles without having to buy new parts, but the only way to be certain is with new, and even then they should be carefully checked.
Good luck--and keep asking questions!