Keep working on the piece I gave you at Chautauqua. Face down, right hand on top… watch the cupping left wrist at the end of the backswing.
Then we're doing work on that downswing. Make 1/2 swings for now.
Record yourself doing those 1/2 swings with the face down for the backswing.
OEM graphite shaft typically will be 1/2" -1" longer than the steel counterpart. So the length will be already at least 1/2" longer than the average mans set with steel shaft.
Your main concern should be the flex and the weight of the shaft, being 6'3" and young, you should try a stronger flex and heavier weight shaft.
I would pull the original shaft and save them for later, reshaft the set of irons with steel shafts. It's a relatively simple job for even a home hobbyist.
If not , get your hands on another set of used golf clubs, prefer came with steel shafts and 3/4"-1" longer from the OEM. Not saying after market job could not do better, but the OEM will take the extra length into consideration and properly reduced the head weight ( lighter badge in the cavity to reduce weight ) making the swing weight correct for the standard D0-D2 for men.
Used set of irons will not set you back too much, that should satisfied your current need until later.