The bike's been sitting since '87. Who knows what shape the internals are in. If everything's good, then I'll reuse the stock bits. If it's in shit shape, I'll use the new bits.
It takes a lot more than just replacing a few parts to properly bring the carbs up to proper running standards. For that reason I'm NOT a big fan of "carb kits."
You should fully break down the carbs, removing all the brass parts including the pilot screws, then soak them in carb dip for several hours in order to properly clean the internal passages.
Then reassembly using new fresh O-rings. You don't typically need to replace jets and such, although replacing the float needles is a good idea if yours are worn. If that's the case then the only decent replacement needles I've found are either Kester or OEM Keihin. You can judge this by watching to see if the needle spring is strong to support the full weight of the carb float without compresing.
short cuts are long cuts when it comes to carbs. For example, the O-rings on the fuel tee are almost always hard and brittle so they must be replaced, and to do so the carbs need to be fully taken apart. Do the job right the first time takes more time, but it saves time in the end and avoids problems later on.
I'm not aware of any way to install a carb kit WITHOUT a complete teardown of the carbs. I feel like that's the whole point. I mean, that's why I bought the kit. Maybe "Carb Rebuild Kit" would've been more accurate. I didn't realize when buying the kit that it was an 'upgrade' from standard jetting, or whatever "Intermediate" is supposed to mean compared to standard.
Bike's been sitting for almost 35 years. Carbs definitely need to be checked out. If it needs everything, it needs everything. If it only needs rubber bits, then that's awesome. Plan for the worst and be surprised when it's not.
This ain't my first rodeo.