Well, that didn't work. Three of the four pieces of epoxy putty didn't adhere to the guide and all of them turned out offset. This is a bit of a shame but some quick work with the belt sander soon removed the residue of the putty.
The reason for the offset is that I've drilled the holes in the tiller off to one side instead of on the centre line.
A short while later the holes are plugged with some Ash dowel that I had and you can see more clearly that the holes are not on the centre line.
The faint pencil line on the tiller shows where the centreline should be and once the glue has had a chance to go off I'll drill two new holes in the correct place.
*** A Short While Later ***
Two new holes drilled and you can see how far off centre were the old holes.
I think I'll stop trying to be clever with fancy bits and just make the thing work. The next update to this project should be when the pins arrive.
Time for a cup of tea.