Spent a good half hour cutting the diagonal down so that it fits to the upper mount point that has already been bolted to the sub-frame. Welded the diagonal into place. My welding is definitely getting neater, although I must admit that these welds are a lot easier to access. The beads are still a little large in places and could probably do with being ground down.
Still can't work out how to get the rubber bush out of the tie bar. A quick check in the Haynes manual suggests using a socket and bench vice to get it in, but to cut it out. Started hunting the web to find suitable replacement. Will probably end up getting a set so that everything is replaced properly.