I don't know the specifics of this question and it was one that I would like to explore myself when I have a bit more free time. Both were brutal regimes and cooperated with each other (along with other nations of the Southern Cone) in Operation Condor, which was essentially a transnational repressive campaign against "subversives." For more on Operation Condor, see John Dinges The Condor Years. One specific incident was the assassination of General Carlos Prats, who was a Chilean general who went into exile after the coup and was later killed in a car bombing in Argentina. Another interesting chapter was the Malvinas/Falklands War. Pinochet was a big supporter and admirer of Margaret Thatcher and allowed British planes to refuel in Chile, which didn't sit well with Argentina. I don't know of one specific book that explains this deeper, but it is mentioned (I believe) in Mary Helen Spooner's The General's Slow Retreat, which I highly recommend! I really enjoyed it, Spooner is a journalist and also has another book called Soldiers in a Narrow Land. The latter explains the Pinochet regime, while the former is what happened after Pinochet was out of power through Michele Bachelet's first presidency. I hope this helped!