Second vote for attempt a rethreading. Nip it to a good bike shop that is local to you and see what they can do - that would seem to fit best with the philosophy of your build so far. Alternatively source a different non-drive side crank arm from ebay and delight in a unique pedalling style!
Will look into it and report back! As I need a new chain ring to compensate for the lack of clearance, and the 122BCD rings are a nightmare to find, it may end up more economic to replace the cranks. Hoping for the latter though.
Second vote for attempt a rethreading. Nip it to a good bike shop that is local to you and see what they can do - that would seem to fit best with the philosophy of your build so far. Alternatively source a different non-drive side crank arm from ebay and delight in a unique pedalling style!