I took Sam Diamond to be Sam Spade. I thought that Falk's girlfriend, Eileen Brennan in this movie looked a lot like Claire Trevor from the vintage noirs.

Good Point
I'd forgotten the impact of 'To Have and Have Not' on the genre era
Unless I've watched it or Big Sleep recently I often blur the Bogey/Bacall interaction
And Spade/Marlowe just brings all kinds of inherent character confusion to the table with Bogey having played Both Iconic Pulp heroes in such short order
as to 'Harry Morgan' confusion funny story when I first Heard of the Harry Potter Novels (mind you this is before the Hype and well before the films) my Brain went to "the old Guy from MASH wrote children's books as for some reason I was cross remembering
Harry
Morgan who'd played Col
Potter
yeah, my brain is kinda wonky like that

The Cheap Detective, another Simon film with much of the same cast takes the Spade/Blaine confusion and Bogart parody up to 11
I would say "Spade / Blaine / Marlowe / Harry Morgan confusion". (That's Harry Morgan, the Bogart character in
To Have and Have Not
; not Harry Morgan, the actor who was in both the
Dragnet
and
MAS*H
TV shows.)

the Heart of Diamond was Spade but being a parody film, they add bits of other iconic Bogart Roles for more jokes
I'd be like some one doing a Rambo Parody and having a few Rocky references simply because Stallone was both
The Cheap Detective, another Simon film with much of the same cast takes the Spade/Blaine confusion and Bogart parody up to 11

Peter Falk plays another excellent tribute/spoof of Bogart and his most famous characters, Rick Blaine and Sam Spade in The Cheap Detective, a film that reunites much of Murder By Death's crew. I can't remember a better evocation of Humphrey Bogart and I'm glad Falk was given the chance to do it twice.
" You ain't running this place, Bert, WILLIAMS is!" Sgt Harris

Ditto.

It's primarily Sam Spade, but there are homages to other Bogart films, such as they "You know how to whistle don't ya?" whic leads into a gag as Eileen Brennan responds.

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Sam Diamond is primarily a spoof of Sam Spade, another Bogie's character, from The Maltese Falcon. There were some clear referrences to Casablanca, but it's Sam Spade - if not for other reasons, just for the name;oD!
"Life is full of censorship. I can't spit in your eye." - Katharine Hepburn