The Boo Brothers are basically ghost versions of The Three Stooges. There is also some resemblance to Casper's regular antagonists The Ghostly Trio, who were probably also based on the 3 Stooges.
This is the only Scooby-Doo animated movie not to involve Frank Welker, whose regular series character Fred Jones was written out.
Shaggy's "truck" is actually a mid-1980s Suzuki Samurai.
Sherriff Busby looks like his voice actor Sorrell Booke, who played Boss JD Hogg in The Dukes of Hazzard (1979). However, his personality is closer to Hogg's right hand man, Sherriff Rosco P. Coltrane.
In addition to his usual wise guy personality, Scrappy Doo compensates for the absence of the Mystery Inc. ensemble, by taking on the braininess of Velma and the inventiveness of Fred.