There doesn't seem to be switch-over code?

From the github link, the new parameters are:

nTargetTimespan: 1 hour
nTargetSpacing: 5 minutes

This suggests a 12 block re-target time, rather than 1 block?

You also use 6 re-targeting periods to work out the new difficulty, so averaged over 6 hours.

I renamed my craftcoin directory to backup and started the client.  It downloads the first 11 blocks and then stalls.

I assume what is happening is that the 12th block (first retarget) has the wrong difficulty, according to the new rules.

You need to have the old difficulty rules up to block 9331 and then switch to the new rules.

An easier option would be to just have a checkpoint at 9331 and skip verification of the difficulty updates until then.