My experience has been pretty tragic. The great set of Aussie Perfornance 14 x 6 jj alloy rims are designed for much longer aftermarket studs and use modern spigot located wheel nuts like used on steel wheels. In New Zealand, most guys use washers and the old shouldered shank wheel nuts. This results in an unsafe wheel because the treads don't engage fully. Even when the sharp edge spigot nuts are used, there is very little thread in contact with the nut, way less than what Ford intended for a four stud wheel in a 6 cylinder 1.2 ton car.
Most newer 108 mm PCD Aussie mags seem to be made to Australian Standard AS 1338 for Escorts and Saabs. The nuts have to come with a more stable sharp edge which 'knife edges' up to the alloy rim. Problem is that these later AS 1338 alloy wheels then have insufficient thread with the stock Cortina wheel studs. They are way to short for safety.
The AS 1338 alloy wheels are much thicker than the stock steel wheels. I had only 6 mm of actively engaged thread. The old factory 13 x 5.5 1977-1980 TE Volante and 14 x 5.5 1981-1983 TF Ghia and S-Pak mag wheels were made with a more common shanked nut, so be carefull when you bolt on newer mags, as you may have to order a set of 16 new studs.
The biggest endorsed tyre (ADR approved) for Cortinas was the 185/70 SR 14's found standard on the 4.1 Ghia and 3.3 S-Pak in the last TF's.
As Sonny said, larger 'mags' require hammer work on the inner lip of the wheelarch. It looks savage, but a quick jack -up of the car, and a bull nose hammer, and you've rolled the spot welded wheel arch back. A sand and palm full of filler, and a prime and paint, and its done in an afternoon.
I ruined one 205/60 tyre on the passengers side front when the stock guard hit it. All it took was the first bump home from orignal owner Mikes house. After that, I ditched the stock 185/70 13 tyres on 13 by 5.5 rims. I reworked the arches, and then got a local Machanical engineering firm to source some proper longer wheel studs. No driving for the last three months as I've been doing some other mods while waiting for the bits to arrive.
As a note, I got 16 new studs and new locknuts this week. 281 Kiwi bucks for locknuts you can only take off with an abrasive disc, and each one needing a 
unique key lock to open. 
