Question: Which two-generation compact automobile was the foundation for the race-class Fitch Sprint?

Context articles: Ford Focus
Chevrolet Corvair
Pontiac Vibe
Shelby GLHS
GM H platform
Corvair Fitch Sprint
Mercury Monarch
Alfa Romeo Giulia
Hudson Jet
AMC Hornet

The Ford Focus is a compact automobile (C-segment in Europe) manufactured by the Ford Motor Company since 1998.
 Designed under Alex Trotman's Ford 2000 plan, which aimed to globalize model development and sell one compact vehicle worldwide, the Focus was primarily designed by Ford of Europe's German and British teams .
 The Focus was released in July 1998 in Europe, succeeding the Ford Escort, and replaced the Mazda Familia-derived Ford Laser in Asia and Oceania along with the Laser-based North American Escort.
 Wayne Stamping & Assembly started producing the Focus for North America with sales beginning in 1999.
The Chevrolet Corvair is a compact automobile manufactured and marketed by Chevrolet for model years 1960–1969 over two generations.
The Pontiac Vibe was a compact automobile that was sold by Pontiac from 2002 to 2010.
 It was jointly developed by General Motors along with Toyota, who manufactures the mechanically similar Toyota Matrix.
 Manufactured by the Toyota-GM joint venture NUMMI in Fremont, California, the Vibe succeeded the Chevrolet Prizm in production at NUMMI and like the Prizm, it was derived from the Toyota Corolla.
The Shelby GLHS was a limited production sport compact automobile from the mid-1980s.
 The main differentiator of these cars from their regular Dodge versions was their use of what would become the intercooled Turbo II engine as well as Shelby Centurian wheels and Koni Adjustable shocks/struts, and changes to the alignment.
The H Platform, or H-body, name has been used twice by General Motors.
 The 1970s H-body was an inexpensive rear-wheel drive compact automobile platform from the 1970s, used for the Chevrolet Vega and Monza and their derivatives.
 The 1980s H-body was a front-wheel drive full-size car platform, and was the basis for GM's second generation downsized full-size cars, such as the Buick LeSabre/Electra, Oldsmobile 88/98, and Pontiac Bonneville.
The Corvair Fitch Sprint was a set of modifications for the Chevrolet Corvair automobile developed by racing driver John Fitch.
The Mercury Monarch is a compact automobile that was manufactured by Mercury from 1975 to 1980.
Alfa Romeo Giulia (] ) is the name of three not directly related models by the Italian car manufacturer Alfa Romeo.
 The first is a line of sporty four-door compact executive cars (Type 105) produced from 1962 to 1978, the second is an updated, mainly up-engined Spider, Sprint and Sprint Speciale Giuliettas, and the third Giulia is a compact executive car (type 952) unveiled in 2015.
The Hudson Jet is a compact automobile that was produced by the Hudson Motor Car Company of Detroit, Michigan during the 1953 and 1954 model years.
 The Jet was the automaker's response to the popular Nash Rambler and the costs of developing and marketing the Jet ultimately led to Hudson's merger with Nash.
The AMC Hornet is a compact automobile which was manufactured and marketed by the American Motors Corporation (AMC) in a single generation from model years 1970 through 1977.
 The Hornet replaced the compact Rambler American marking the end of the Rambler marque in the American and Canadian markets.
 Hornets were also marketed in foreign markets, as well as assembled under license agreements with AMC that included Vehículos Automotores Mexicanos (VAM), Australian Motor Industries (AMI), and by Toyota S.A. Ltd. in South Africa.