I'll weigh in here for some comments. I'm sure Chicago has lots of info about this.

IMO, Humphreys had a great criminal mind. According to the literature he would much rather "pay someone off" as opposed to killing them . He also detested publicity. He was apparently a likable person who got along well with just about everyone.

Humphreys was involved in the famous Ricca pardon that resulted from the Hollywood Extortion case. A lot of strings were pulled to get Ricca an early pardon. Accardo was also heavily involved. I would highly recommend reading this story.

Humphreys also spoke freely to the top echelon guys. He appeared to have no problem expressing his opinion to Ricca, Accardo and others. He cautioned Accardo about the big mansion saying, "you'll stick out like a sore thumb." "The good money doesen't go to the suburbs." Accardo didn't listen and later regretted he purchased the house. He (Accardo) said he should have listened to Hump.

Mad Sam was another person who irritated Humphreys. Sam's erratic behavior drew too much attention and Hump expressed his displeasure to Ricca and Accardo. He also cautioned Ricca and Accardo about Giancana not showing up for meetings and creating a lot of publicity for The Outfit. There's also an incident at the Armory Lounge where Giancana had one of his men go to the parking lot and talk to FBI agents.

Accardo was another benefactor of Humphreys' talent. Accardo was convicted of falsifying his tax return in the late 50's, and was convicted for counting his little red Mercedes as a tax write-off. Judge Julius Hoffman sentenced Accardo to something like 6 yrs in prison and fined him $15,000. The Hump went to work on the appeal, and in the fall of '62 Accardo's conviction was overturned. Paul Ricca was not as lucky. He was convicted (income tax) in '59 and served about 27 months in prison. Ricca would be charged for income tax problems again in 1965.

M. Humphreys is another example of why The Outfit was so successful (IMO). He was not eligible for the top position in The Outfit because he was not Italian, but his talent was certainly a factor that could not be ignored. He died in 1965 from a heart attack. The FBI just about drove him crazy. They followed him everywhere and "dogged' him for years.

There is an abundance of info in the FBI files about M. Humphreys. Gus Russo also devotes a large section of his book to Humphreys. All the above listed info came from FBI files and Russo's book- The Outfit.

I believe most people Would agree that Murray Humphreys was the greatest political fixer of all time.

I'm not sure about Jack Guzik. I've read about Jake Guzik who was the financial wizard for Capone and later Ricca, Accardo and Giancana.

There's an interesting story about Jake Guzik being kidnapped in the 30's or 40's.
Apparently Accardo and Giancana didn't think Guzik's math was right, so Giancana "grabbed him." He was held for a short time and released. Someone reported to police that he had been kidnapped. When questioned about the incident, Guzik said he was visiting a family member. Not sure about this story, but I did read it somewhere.