My '72 TC certainly has the smaller Spitfire/Herald hubs and bearings, so that means the smaller stub axle as well. As far as I know, that carried on to the '73 TCS until Lotus stopped making them. But this is Lotus, so nothing is ruled out....
I don't know about the upright/vertical link casting. I've never looked that closely at them but was under the impression that the upright castings are the same for both Spitfire/Herald and GT6 it's just the stub axles are different, so one has a bigger hole than the other. I don't honestly know though, so if anyone does have an answer then I'm interested to hear for sure either way.
The 2 seat Elan does have the situation you mention though, where if the Elan has bolt on wheels like the early ones then it had the Herald axles/hubs. If it has knock on wheels as most of the later ones did, then it has the larger axles & bearings. And it's quite common to convert the type 14 caliper & 9" discs to the larger type 16 caliper & 9.5" discs as fitted to the GT6, Elan+2. A simple bolt on mod. I have been mulling over whether that's an option for the TC or whether to just bite the bullet and spend money with Hispec and get their version of th e4 pot Princess caliper.
I know Richard does a conversion kit which looks good value for money as it includes everything you need including new alloy hubs. I'm just not sure I want to go with custom drilled discs, I do like to stay with parts I can just buy from a motor factor over the shelf. I'll be interested to hear what's involved in the set-up you're exploring, when I read the "machining needed", I just turned off.....
Brian