Non-trap door trans swap

Long time no post.
Sorry about that. Past 7 or so years I've not been riding my 52K but once or twice a year.
I've been trying to sell it and hauled it down to Daytona and put about 800 miles on it.
Now I seem to have a tooth or two missing in 1st gear.
As I recall the 54 and up trans will fit in the early cases.
Is my memory correct?
What else needs to be changed to do the swap?
I see many trans for sale saying model K / Ironhead, is that correct?

Thanks for the help guys.
Tony

[Dusty-Dave]

Ifn memory serves the tranny in early Iron heads that released the clutch the same way as a K will work. Once they moved the clutch release to the other side the mainshaft wont work.
Dusty