I had a rake about in FamilySearch.
1869 census of Argentina, Pergamino
José Macallister, 27, Irlandes, Dublin, Estanciero
So he was born in Dublin (town or parish or county?) in 1841/2.
On a different page, but still in Pergamino
MacAllister Anita, 27, Argentinia, Buenos Aires, Estanciera
1895 census, Pergamino
MacAllister Martin, 20, Argentino, BA, Estanciero
MacAllister Carlos, 22, Argentino, BA, Estanciero
MacAllister Maria, 25, Argentina, BA, Proprietaria
MacAllister Ana, 16, Argentina, BA, Proprietaria
MacAllister José, 12, Argentino, BA
Still Pergamino, but a different page
McAllister Juan, 35, Irlandes, Estanciero
Tobim Maria, 33
McAllister Mariana, 10
McAllister Brijida, 8
McAllister Juan, 6
McAllister Guillerm, 4o
McAllister Arturo, 2
McAllister Ramon, 1
All Argentinian and born in BA.
So if this is Joseph's nephew, he was born in 1859/1860.
(There are also a 35-year-old Henry and a 30-year-old A MacAllister, both born in England, in the 1895 census.)
Guillermo MacAllister, 39, son of Juan MacAllister and Brigida Keeling, married Margarita Seery in BA in 1895.
Noting that Juan MacAllister in Pergomino had a daughter Brijida, it would not surprise me to find that the parents of Joseph's nephews John and William were John MacAllister and Bridget Keeling.
Aha! Juan MacAllister, son of Juan MacAllister and Brijida Keeling (mistranscribed Reeling) married Maria Tobin in Pergomino in 1885.
John M and Bridget Keeling had Christopher, 1857; John, 1859, Donabate, Co Dublin; Mary Ann, 1864; James, 1866; Patrick Joseph, 1868; Jane, 1870; Eleanora, 1871.
Juan MacAllister, 5, son of José MacAllister and Anita Fox, died in Pergamino in 1876. There are other references to Ana or Anita Fox or Fose (probably mistranscribed) as mother of assorted M*cAl*sters. So it would appear that Joseph MacAllister's wife was Anita Fox.
Could the forebears of either Anita Fox or Bridget Keeling have come from Fife? Or Joseph's mother, whoever she was?
.... Getting a bit speculative now, but Joseph, son of Charles M and Mary Quinn, was baptised in Donabate, Co Dublin, in 1838 .... a few years adrift, but the same place?