Chubby Carmichael is clearly modeled on Roscoe "Fatty" Arbuckle, whose acting career was wrecked by a false murder charge.
Perry's girlfriend Lupe looks to be based on Florence 'Pancho' Barnes, legendary pilot. After landing her plane she passes by a sign that says "Bottoms Up". Pancho operated The Happy Bottom Riding Club, a dude ranch, restaurant, and hotel outside Edwards AFB. The club, and Pancho, were featured in the novel and movie The Right Stuff (1983).
The studio head, Walter LeBaron, is based on William LeBaron, who was the head of production at Paramount in the early 1930s.
Ptomaine Tommy's, where Perry Mason first appears, was a real restaurant in LA. It was the originator of the "chili size", an open-faced hamburger smothered in chili.
Sister Alice appears to be based on Aimee Semple McPherson, evangelist and founder of The Foursquare Church.