There is an article on welding the clutch pedal ear( cut from the original bellhousing where the clutch petals etc attach) on to a later bellhousing . Trying to remeber if it was a late 235 /261 or a late six / v8 bellhousing.May have been another site but that has been done also -
also - the 4 speed MAY bolt up to the later housing - Is the clutch a 10 spline??
All that being said - the 235/261 is more than likely the easy road. BUT - I do love my late 250. Can usually be had for a song from the local pick your part cuase everyone thinks they must have a v8.
LMD