In my experience, the only time one need fear slicks is when the track is wet or greasy. On a dry surface, they'll make you feel like Superman compared to anything treaded.
There are racing classes which require tires with a DOT treadwear rating of 200 or above, and about a dozen makers building tires specifically targeted to that market. They cost ~$250 each, and generally only come in larger-diameter sizes as is fashionable these days - not really what you want.
Several "race-tire" manufacturers build treaded tires which are made specifically for classes which require a "DOT" tire but have no minimum treadwear rating. Since it costs money to undergo each section of the testing, tire-makers can forego the treadwear part and pass the savings on to the customer, hence the existence of "street-legal" tires with a DOT treadwear rating of 000 - or as I call them, "cheat-stock" tires. Even in the softest pavement compound these are expected to last through a few weekends' racing on a full-weight (~2500lb) car so they might hold up for a year on a lightweight.
As a rule, you want to run a wider rim for racing than you'd use for the same width tire on the street. By pulling the sidewalls out, they're stiffened which improves the tire's stability. For street use, a 205/50 or /55 would normally call for a 5½ to 7½" rim but for racing you'd want 7-8". So, 7" would be tolerable but personally I'd go with 8" (or come down to a 195 tire).
http://www.yokohamatire.com/tires_101/c ... eel_width/
Stock "Karmann-Ghia" front calipers may or may not fit inside a 13" steel rim - it depends upon the backspace and the shape of the inner "bell" of the rim. You can grind a bit off of the caliper if necessary, but typically only ~¼". Drum brakes should be adequate in the rear. Ford Pinto/Mustang II discs work inside most 13" rims; they have a 4x4¼" bolt pattern...that takes care of the front but it takes custom drums to make the rears match. All things considered, 4x100mm is probably the best choice for a lug pattern simply because it is so common (and 4x100 rear VW drums are readily available from the aftermarket).
Can't afford the rare and extreme car of your dreams? Well just build one.
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