How hard is it to change a starter in a 340 Duster?

If you’re putting a new starter motor in, consider installing a mini starter. Much easier to install (space wise) compared to putting in a regular size starter.

Do a search on here for tips on replacing starter motors as there have been many threads on it already including what part number to buy for the mini starter.

This gives you an idea of the size difference between the two starter motors:
340 Manifolds on 318