So finally had a chance to get into the garage to sort the worn bushings out and try the tool i made. I made a couple of modifications including adding clearance where it butts up against the wishbone as some have larger welds than others, and also to make a custom nut with a very long thread to try to avoid stripping threads. This also makes it easier to use as a socket no longer needs to fit in. I can confirm that it worked - I knew two of the bushings were worn, but ended up replacing five as I found some of the others were worn. This was all I had to hand and I haven't even started on the rear suspension yet.
Photos are the tool with modifications, the tool in use for removal, and the end result with the removed bushing on the tool. Installation was easier than removal. I changed the front upper bushings on the car without removing the wishbones so it ended up being relatively easy. I don't know why this worked when others have needed so much force for removal, but there was no significant rust at all so maybe that made it easier?