Syncing the carburetors will make a big difference I bet you.
Have you put any air into the forks? Air them up to 10 or 14 psi and see what happens to the clunking. Since the downtubes are pitted they may not hold pressure long, but I bet you will see a difference as long as it holds pressure.
Try Race-Tech or Forking by Frank for downtubes, they aren't cheap.
Jack up the front of the bike. Have it so the front wheel is a bit off the ground. Try grabbing the bottom of the sliders standing in-front of the bike, and attempt to move them forward and back. Is there any back & forth movement, any clunking? If so, loose/worn steering head bearings.
Next try moving from full left-lock to full right-lock. Do you feel any notchiness as the forks move side-to-side? That's called
brinelling. Imperfections in the races from being loose, or from too-many hard wheelie landings, two common causes of the notchiness.
New rubber donuts for the top bellmouths of the carburetors, or those to the VBoost manifold will make things easier to mount the carbs and the airbox. In the meantime, consider using some water-soluble gel from the drugstore to help things slide. Some reading for you:
https://www.vmaxforum.net/threads/seat-those-carbs-easily.21303/
Here's something from an earlier post:
There's an easy way to get your airbox mounted and this is how:
Assuming your rubbers are in decent shape, no rips, tears, or cracks which would cause leaks, simply place the assembled airbox above your carbs. Start them onto the carb bellmouths. Now you need to have the bike on the centerstand. Step onto the footpegs and move your position forward until your butt is resting on the airbox lid.
Gently lower your weight onto the airbox lid, and you should feel your airbox pop-into the carb bellmouth rubbers. Climb off and confirm that your airbox is now in-place. You can use some water-soluble gel like KY (yes, that KY) and place a thin film onto the inside of the rubbers and the mating airbox surfaces to help 'mate' the pieces (no pun intended). Remember to replace the KY where you got it from.
This works for me with older rubbers when you cannot seem to get them to fit. Some people say, "boil them in water to soften them up, and quickly place them into position, and press the airbox down." I bet that if you try the persuasion of your butt on top of the lid, you won't need to boil the rubber rings.
I call it the Happy Days Method: "sit on it Potsie!"
I don't know that the mystery parts are from your bike.
New OEM friction discs are what I recommend. You can replace the innermost friction disc, which is half-width, with a 'regular' full-width one. There are several parts you eliminate when you do that. You can search for threads discussing that. One was recently done by DocDoom, which gives a good explanation of doing a clutch replacement.
https://www.vmaxforum.net/threads/question-sanity-checking-on-upcoming-clutch-job.53162/
CaptainKyle did a video:
https://www.vmaxforum.net/threads/gen-1-clutch.52836/
so between those you should be able to get it done properly. You do NOT need to go aftermarket! Sean Morley I think offers a stronger diaphragm clutch spring, if you want to work on your forearm muscles, by all-means use two OEM diaphragm springs, stacked together (referred to as the DD, or 'double-disc.' Get your mind outta the gutter!). If you had a large-displacement engine, or a power-adder (NOS, supercharger, turbo) then one of those might be worth the expense. Otherwise forget it.