Is the inboard end of the flat gear different between straight-tails and slant-tails?
The part number is different between the two, but that may just represent the different bolt pattern at the axle end. I'm wondering if, mechanically, the later flat-gear would bolt up and fit in the earlier fuselage. The landing gear bulkhead is the same between the two, so it just might work.
Of course, getting 337 approval might be difficult since the part numbers don't interchange between the two aircraft.