Ralph Byrd, who had previously played Dick Tracy in four serials Republic produced in the late '30s and early 40's, was hired to replace Morgan Conway because, after the two previous films (Dick Tracy (1945) and Dick Tracy vs. Cueball (1946)), exhibitors complained. To them, Byrd was Dick Tracy, and only Byrd would do. RKO accepted this and hired him to finish the series. Unfortunately for Byrd, because of this he spent his career typecast as Dick Tracy.
The third of four classic Dick Tracy movies.
Longshot Lillie drives a 1941 Oldsmobile coupe.
There's no proof that Ralph Byrd was typecast as Dick Tracy, not being able to play other roles, because he died at 43 years old... right after the 19050's TV series... and there's no telling what his future career would have brought.