Registration in Illinois under this type of provision denotes the car's YOM as the "year the car resembles" (ex: 1957, 1958), the "make" is the manufacturer of the body (Vintage, Intermeccanica, etc), the "model" is what the car represents with the word "replica" at the end (Porsche 356 replica, Speedster replica, etc.).
It's fully legal, and even eligible for antique plates (less than 20 bucks for 5 years).
There are some pre-registration hoops to jump through, and it's impossible to jump through them all without some time elapsing between the purchase and registration dates (which caused me to incur a penalty for "late payment of sales tax"), but all in all-- it's a great program, and makes much more sense than the circus California has going with the 500 exemptions a year.
From my Illinois experience, this really is good news for VA enthusiasts.