Gearbox damage

So I managed to lay the two engines out next to each other yesterday, firstly to look for any obvious signs of damage to the gears, and also to swap various bits from the current to spare engine, such as oil cooler couplings, mounting frame and billet sump.

With the sump off of the damaged engine, I used a pair of mole grips on the selector shaft to index through to fourth gear. All gears engaged as they should, but as soon as I turned the output shaft when 4th was engaged, I could see the selector fork moving out of It's position. If I held the fork in place, 4th gear would engage correctly, and I soon realised at that point that the selector drum was damaged. The tip part of the profile slot had been smashed off, thus allowing movement lateraly of the fork, allowing 4th gear to disengage. I know my writing probably makes this description twice as difficult to understand as it should be, so I'll try and get some pictures up to aid the explanation.  I'm just wondering now if the drive dogs are still intact, there was certainly some swarf build up on the oil strainer. Do I just swap the selector drum out and hope for the best, or go the whole hog and replace 4th and the selector fork too?