Thinking out loud.
If Castro was involved I don't think it would have been directly. Most likely is he would have used a page from the CIA's play book and found a willing domestic opponent.
The domestic conspirators duplicitously accept Castro's assistance.
Plan "B", if the attempt on JFK fails, the blame falls on the Cubans with LHO a willing accomplice. The Carcano in the TSBD leads to Ozzie, the Mauser to the Cubans.
Plan "A", if the attempt succeeds, the LN patsy takes the blame.
If Castro was involved I don't think it would have been directly. Most likely is he would have used a page from the CIA's play book and found a willing domestic opponent.
The domestic conspirators duplicitously accept Castro's assistance. Or, the willing domestic opponent found Castro. In 1959, in southern California, LHO reportedly made contact with the Cubans and his desire to go to Cuba to help Castro could have been communicated.
Reports of Castro's newfound "best buddy," Khrushchev, were most likely seen by LHO in the newspapers, and this relationship could have been a part of LHO's desire to go to Russia. Some of Castro's intelligence agents were reportedly trained in Minsk while LHO was there. It is feasible that LHO had some contact with some of the Cuban agents in Minsk. And they could have convinced LHO that he could best support Castro's regime from the USA, hence his desire to go back.
Although the idea of a Texas trip for JFK had already been tossed around for a while, actual planning began in June of 1963. Castro had at least one spy that was reportedly placed in a high position in the pentagon. It is possible that word of a Texas trip in the planning stages reached this spy between June and the end of September (when LHO went to Mexico City). Therefore when LHO tried (in vain) to go to Cuba through Mexico City, they might have convinced him to go back and stay around Dallas in hopes that he could make an assassination attempt when the JFK visit happened. If LHO, while in Mexico City, had told them about his attempt on Walker (as part of his resume), they might have realized that he had the capacity to take on the task of an attempt on JFK (as a lone assassin).
Just as LHO apparently "fell into the lap" of Castro at the opportune time; the employment at the TSBD and the motorcade route in front of the TSBD apparently "fell into the lap" of LHO at the opportune time. LHO had the phone number of Duran and, once everything became apparent and he had devised his plan, all he needed to do was call her and let her know to be watching...
The domestic conspirators duplicitously accept Castro's assistance.
Plan "B", if the attempt on JFK fails, the blame falls on the Cubans with LHO a willing accomplice. The Carcano in the TSBD leads to Ozzie, the Mauser to the Cubans.
Plan "A", if the attempt succeeds, the LN patsy takes the blame.I haven't seen any evidence of others shooting at JFK in Dealey Plaza that day. I believe LHO was capable and acted without assistance.