The Mystery Hideout by Ken Follett, 1976.
The first time Mick Williams meets Randall Izard (called “Izzie”) is when the news dealer Mick works for asks him to train the new boy on his paper route, and Mick learns that Izzie will also be going to his school. Mick doesn’t like Izzie much at first. The new boy speaks with a posh accent and is riding an expensive bike that he says was a present from his father, who makes television ads for a living. Mick doesn’t have a father, and he stole the bike that he rides for his paper route.
Mick guesses that Izzie’s family used to have more money but have fallen on hard times, which is why Izzie needs the paper route. Mick is worried about his own future. Someone is building a new hotel on the street where he lives by knocking down the old film studios, and his mother says that they’re going to demolish all the old apartment buildings around it. That means that they’ll have to find a apartment, which isn’t easy because they don’t have much money, and not everyone wants to rent to a lone woman with a child.
Mick kind of envies the criminal gangs that he reads about in the paper, like the Disguise Gang. They stage daring raids on banks while wearing clever disguises so that no one knows that they really look like. They fool everyone and get away with tons of money. Mick wishes that he was that clever! If he was, his mother would never have to worry about money again.
But, Izzie turns out to be a good friend for Mick. They both love to play soccer, and Izzie tells Mick that his father used to work in the old studio buildings that they’re tearing down to build the new hotel. In fact, Izzie even knows a secret way in, so the boys sneak in to explore a little. They’re goofing off with some of the props when they make the startling discovery that the prop guns are loaded with real bullets! Then, the boys have to make a run for it because there are other people sneaking around the old studios. What is going on there?
This book actually takes place in London. I don’t think they actually say the name of the city in the story, but they do mention the Thames, the money is all in pounds, and there are children playing cricket. But, it’s the kind of story that could take place anywhere. Mick and Izzie are realistic characters. Both of them are worried about their families’ hard times. Mick in particular wants to be the man of the house and to help his mother in her struggles to provide for them. His inner debate about which side of the law he should be on is also feels real, and it’s satisfying what he chooses when he realizes what criminals are really like and the danger they pose to people he cares about.
The Adventures of the Red Tape Gang by Joan Lowery Nixon, 1974.
The Secret Summer by Ruth Chew, 1970.
The Ghost that Came Alive by Vic Crume, 1975.
They tell the kids that the house is supposed to be haunted and people can often hear the ghost of Andrea Cliff calling out in the night. The kids soon hear this spooky voice themselves, calling for help. Trapped in the house with the ghost and unfriendly people, the Blairs decide that they have to figure out what’s really going on, but the danger is worse than they know, and Jenny’s premonition of doom is getting stronger all the time . . 
The Mystery in Dracula’s Castle by Vic Crume, 1973.
Alfie is an aspiring film maker. Specifically, he wants to make horror movies, and he talks his younger brother into playing the part of Dracula in his latest Super 8 film. Leonard is only a reluctant vampire because he doesn’t like horror movies. He really wants to be a detective, like Sherlock Holmes. Back home, he and his brother saw police investigating the scene of a robbery at a jewelry store, and he’s decided that he wants to investigate crimes like that. Soon after they arrive at the beach house, Leonard adopts a stray dog and names him Watson so that he can be his sidekick.
Jestress's Forgotten Books and Stories 