The drive train was the same for all models (USA versions - I'm not sure about other versions). Graduate, Veloce & Quadrifoglio were trim level variations.
In the US, at least, the Series 3 cars were also separated into different trim levels at different times in the run:
In 1982, you had the Spider 2000 and the Spider Veloce (pronounced vel-OH-chay). The 2000 had steel wheels, vinyl seats and a vinyl top, while the Veloce got alloy wheels, leather seats and a cloth top.
In 1983 and 1984, there was just the Spider Veloce.
In 1985 the line was split into three models, the Graduate, Veloce, and Quadrifoglio (pronounced "kwah-drih-FOH-lee-oh"). The Graduate was the "introductory" level of trim, with vinyl seats, vinyl top, and steel wheels. The Veloce came with leather seats, a cloth top, power windows and power external rear view mirrors, and very attractive "star" alloy wheels. The Quadrifoglio came with specially designed leather seats, canvas top, "phone dial" alloy wheels, a/c standard, special carpeting, a redesigned front spoiler and tacked-on "side skirts", and a detachable hard top.
Veloce is a state of mind and marketing after 1965-67(?).. if someone called you on it, it's strictly ill-informed driven. If they can't explain to you why your car is performance wise less ( not a Veloce) than it is, then move on to the bar and ignore the maroon.. In the Canada and everywhere else for that matter , there was no pecking order just perhaps, marketing from one year to the next. Trim had nothing to do with it...lesson here is just call the car what it is ... a 2 litr Spider... either of Euro or US spec.... if that is important.
Veloce is a state of mind and marketing after 1965-67(?).. if someone called you on it, it's strictly ill-informed driven. If they can't explain to you why your car is performance wise less ( not a Veloce) than it is, then move on to the bar and ignore the maroon.. In the Canada and everywhere else for that matter , there was no pecking order just perhaps, marketing. Just my opinion.
At least for the Euro models of that era, a Spider or Spider "Junior" usually had a 1600 engine, and a "Veloce" had a 2000.
In the US market, all post-1971 S2 models were 2000's, and they all lost power as emissions controls became tighter: a 1972 Spider Veloce had about 15-20 more HP than a 1979 Spider Veloce.
The Junior came as a 1600 or 1300, lacked the centre consul, opening 1/4 lights, headlight cowls and had a metal dashboard like in the Duetto, it was made down to a price for tax reasons. I believe later Juniors had a trim level more like a Veloce.
My S2 Spider Junior has now a 2000 engine and rear axle fitted.
Alfa had a hard enough time selling cars. They didn't need an entry level car as an enticement .. The Graduate with roll up windows was a brainchild to fill that niche that failed.. It was idiotic for them to build a lesser motor and drive train for it and call the car a Spider Ti or Normale...so they called it a Dustin Hoffman Graduate. ..with all the same motor as every other Spider... Veloce or not.. Same brains went into the marketing of the Nikki Lauda disaster than cost NOTHING but decals and a couple badges. They made engines all the same to survive... not to make the production more complicated and less cost effective by offering performance packages on an assembly line of limited volumes. They were not producing variants like Corvettes. The scale of production never warranted it.... unlike GT Juniors and GT's in the late 60's when the home market ruled..