Had a 3207 many years ago -- wonderful boat!
I was ~6'3" back in those younger days - agree that bunk was at least a few inches too short to allow stretching out b/o bulkheads at both ends.
The port bunk, however, was designed to pull readily toward the middle of the aft cabin to make a comfortable larger (almost full size) bed (with a filler toward the outside).
In that position, the inboard side of the bed is freed from the forward bulkhead of the aft cabin, now extending partially over the stairs.
Tho' the stairway passage was narrowed by the overlap, it was accessible, and the area between bunks was still enough to walk back to the aft head.
I slept with my feet slightly off the inboard end of the bed then (extended over the entry stairway) so many nights it seems like only yesterday . . .
That said (sorry to be so wordy) -- if I could do that fully extended and comfortable (with feet off the end no longer constrained by the bulkhead at the foot of the bed), you should be able to fashion a [removable] extension that provides full support for 6'5" or more.
(Probably impossible for anyone to visualize from my description except for the 3207 skipper, who will easily understand my description.)
Perhaps try an extension that is supported at its end by a cabin step at the foot (forward) end of the aft cabin?
Good luck -- well worth the modification innovation and trouble . . .
John