The Resto-Cal (or Resto-Custom) Look is predominantly based around a stock-bodied car (i.e - no body mods) that has been lowered front and rear. The general consensus is - the lower the better! One spline at the rear is considered the minimum!
Wheels can remain stock, or other popular options are Polished/Chrome Empi 5s (it's all about the Bling!) or Early Porsche Fuchs.
Interior is stock, except for the possible additions of a performance shifter or additional accessories (e.g - Bambus parcel shelf)
Period accessories are popular - think along the lines of fender skirts, roof racks etc. Big engines are not necessary, but it's also not unheard of for a Resto-Cal car to have a hi-po motor. Narrowed beams are popular too, narrowing the front track to enable the car to go lower, giving a "tucked" look.
The Resto-Cal look is a vintage style, resulting in a car that has a ground scraping stance but can be restored to stock relatively easily should you wish.
Any model of aircooled VW can be given the Resto-Cal treatment (except perhaps for the MacPherson strut models) Pre 67 cars are more traditionally popular, but late models are increasing in popularity.
The German Folks Klub is perhaps the world's most famous Resto-Cal club: thegermanfolks.com
RestowagenUK.com is a site dedicated to UK Resto-Cals: restowagenuk.com