The changes from the oval track to roadrace/hillclimb are less than you might think - and many of them were accomplished with suspension adjustments and spring/shock changes.
Many oval cars use a "spool" in place of the differential - This car was a lucky find on E-bay/racing junk.com, which already had a "True Trac" torque sensing differential in the Winters quick-change rear.
Kevin put in the Lajoie "confinement" seat, and upgraded to a Sweet Mfg. collapsible steering column. The transmission is now a standard wide-ratio M21 Muncie (the stock car guys take out 1st and 2nd for less driveline inertia)
It is very similar to the Wilsberg/Jarzombeck "Cavalier"#5 in this gif :
To be clear - "Modifieds" have evolved from the "Sportsman" full size coupes of the 60's, while "Supermodifieds" evolved from the more radical "cutdowns". Modern "supers" are the poor man's F1 - 900 methanol-injected horsepower, direct drive *1800#, 2 G+ cornering with wings that directly load the wheels - a pic of the Vic Miller/Chris Perly #11, current ISMA champion
*direct drive = no clutch, flywheel, transmission, or starter - push start with a truck!