Turns out the conversion is not straightforward at all! Going from SD31s on 3JH series engines to SD60 is very difficult apparently. Also there are no SD60's available until at least August at the earliest.
According to Minnards there was a conversion plate for SD31 to SD45/50 but there is not one for direct from SD31 to SD60 so its either get one machined or buy a complete engine
fibreglass mount and cut the old ones out and put the new ones in!
So as per my other thread the hunt for SD31s to cannibalise continues.