The rack (externally) is basically the same used on the Triumph Herald/Vitesse/Spitfire/GT6 so they should fit. The boot stretches over that large coupling, especially if you wipe it with grease/oil before fitting.
Getting the right size isn't difficult. I must admit I normally keep a set of "universal" boots on my shelf and that's what is on my car at the moment. These are the same diameter as the tie rod on one end, with the rack end being a longer length with several sections of reducing diameter at the other. Select the diameter you need for the rack, cut with a sharp knife and that's it. I also use tie wraps to hold them in place....
Brian