Haig,
According to Joe Rusz’s article in
Porsche Sport 72, the wheels are: “…American magnesium wheels.” and “American Racing mag wheels”
Front: 7” with Goodyear Sports Car Special 5.00/9.20-15.
Rear: 8.5” with Goodyear Sports Car Special 5.25/9.50-15.
Boschen & Barth* report: “Goodyear tyres, 5.00/920-15 and 5.25/950-15, were mounted on the 7 and 8.5 in American-made rims.”
They also note, “The three-year conversion was estimated to have cost $15,000.”
*Boschen, Lothar and Jurgen Barth; Peter Wareham, trans.; ed. Paul Frére and Michael Cotton;
Porsche Specials; (Wellingbrough, Patrick Stevens, 1984); 184-185. ISBN 0-87938-227-9
These authors may have a lot more material than they published. It is worth contacting them.
Goodyear seems to make suitable (new) vintage race tires.
http://www.racegoodyear.com/tires/pdf/Sports_MSRP_05JAN11.pdf
They are still ‘Sports Car Special’ but have ‘Eagle’ on the sidewall. I think the ‘Eagle’ can be ground off without damaging the tire. This then would appear exactly original. You might try this on some worn out take-offs first.
I suspect you can ‘barn find’ old hard originals sitting in some garages but those should be for static show and never driven. One might serve as a guide for detailing current tires.
(I was at the Indy Speedway Museum once, talking to the curator as he was airing-up an early ‘70s Champcar. AJ had taken it out on the track
at speed on those decades-old tires. Not me.)
Best,
Grady