There's a discussion at the Surly's Google group about putting on an LHT frame a fork with more rake than the standard one has (43 mm) to make of it a French randonneur style bike. I am wondering if this really could be so simple or rather if there isn't much more to do to turn a LHT into a low trail bike and have it handle well. After all, wasn't the whole frame designed with high trail in mind?
As far as the steering is concerned it is the front end that is doing the heavy lifting. If your target bike also had a 72 degree steering angle, putting a different fork on it would get you there, but the fork has to be designed to have the same height, the extreme would be putting a 29er shock replacement rigid fork on there!
Kogswell did a lot of messing around with fork angles and even stocked some Porteur forks with different angles in various wheel sizes.