Just re-read thru the 3 pages of threads to get "reaquainted" and am still liking that 58. When they first came out back in the day it was so much of a change from the previous tri-five years and kinda soured me back then originally. Now, not so much, love the one year only look,
How we do change huh? Be glad that the body is in great shape. Not sure how much after market support there is for one year only body panels.
You mentioned about wanting a rear end gear change or a newer "chunk". Do you know what gearing you have now? My 57 2 dr. post has a 283/stock 57 dual four Carter WCFB 4 bbl carbs, Muncie 4 speed and a 3:55 posi rear end. Seems to be pretty good on the road last I remember but has been awhile since I've been able to drive it. Still tied up in paint/body process.
Earlier you mentioned having a 3:36 gearing which would be the standard offering unless changed or optioned to a different gearing when ordered. Either a 3:36 or 3:55 I was told would be a good original 55-64 10 bolt 3rd member drop out style gear for highway use. Maybe look for a 3:08 for better hiway cruising but low end would suffer some.
Again, loving this thread and hope you are able to keep it with the condition and family history it has. Good luck in your quest.