All back together, did a quick fishing line wheel alignment (easier on a hoist) and took it for a spin today. Feels a lot better with the extra castor and urethane bushes, has a real go kart feel now and wheel centres much easier on the straight. Steering is maybe just a touch heavier - not sure how it would feel if you had a manual rack.
Final rack spacing I went for was the 12mm lower than stock, and a 10mm cone spacer with the rod end. I also machined the head of the bolt down to a chamfer to get enough misalignment clearance and meant I didn't need another spacer in there.
