Hi Nick,
This is very timely since I am in the middle of replacing my S2 1600HF tyres and also deciding on the future of my wheels (Cromodora 14x6J).
The Owners handbook specifies Michelin XAS 175 14. Their profile is not explicitly given, but in its absence you can assume that is 80%. I have been using a 175/80 Firestone tyre, but the Michelin XASs are now available from Longstone Tyres (Wangler has provided a link) and I have just bought a set. Putting them alongside the Firestones is interesting - the XASs have an asymmetric tread pattern (the outer and inner faces are marked) and a rounded shoulder - the Firestones are quite square in comparison. My Firestones are also over 20 years old (with surprisingly little wear, so they must be a very hard compound), and I am hoping the new tyre will make the steering a bit lighter at low speeds on grippy surfaces.
The rims are more of an issue. The tyre shop who removed the old covers were concerned that I had been running them without an inner tube, since the Cromodoras lack 'safety ridges' inboard of the rims. These are intended to stop the tyre deflating if it is hit from the side near the rim. Tubeless tyres were introduced around 1970, but it was a while before safety ridges were introduced and the Cromodora design was never updated. The valve holes are also thicker than would be found on a normal tubeless wheel, which have a recess. My valve holes were also pitted but contained sufficient sealant to avoid any leaks.
My Cromodoras were last refurbished 25 years ago so it was also time to visit some paint shops to see what could be done. In short, it is not very much. The Mg-Al alloy wheels are too delicate (and the old paint and filler too thick) to be bead blasted. An exploratory test showed the surface underneath was quite pitted and some of the detail ('Cromodora 14x6J') and sharpness had already been lost and not just painted over. The advice was to get them chemically stripped but that should not involve alkali ('soda') or strong acids. The only remaining choice is to use methylene chloride - the sort of paint stripper that has disappeared from use because of handling, disposal and safety issues. I used a lot of it to take my car back to bare metal in the 1990's so I know how unpleasant it is and it is not something I look forward to revisiting in a small garage with a recently repainted car.
My solution has been to buy a set of 4 reproduction Al-alloy wheels from Pieces Fulvia, which arrived today. They have a safety ridge and a recessed valve hole, so are designed for tubeless tyres. In fact, my tyre shop tells me you
must not use tubes in wheels with safety ridges. I will use the best Cromodora (with a tube) as a spare while I wait for Spring to clean up the rest in the open air!
Good looking car too,
Glyn
P.S. There is a very good article on the process of Mg-Al wheel restoration here:
https://stevekouracos.com/restoration/tips-and-tricks/aluminum-magnesium-wheel-restoration/