I don’t see any difference between the full paragraph and the excerpt from the Catholic Answers tract.
From the paragraph:
“…they still dare – a false bishop having been appointed for them by, heretics – to set sail and to bear letters from schismatic and profane persons to the throne of Peter, and to the chief church whence priestly unity takes its source; and not to consider that these were the Romans whose faith was praised in the preaching of the apostle, to whom faithlessness could have no access.” (Letters 59)
From the Catholic Answers tract:
“Would the heretics dare to come to the very seat of Peter whence apostolic faith is derived and whither no errors can come?” (Letters 59 , 14).
Comparing both translations we have:
paragraph: heretics – to set sail and to bear letters from schismatic and profane persons to the throne of Peter
tract: would the heretics dare to come to the very set of Peter
These are practically identical.
paragraph: whence priestly unity takes its source
tract: whence apostolic faith is derived
Depending on the original wording, priestly unity can probably be translated apostolic faith. Rome was and is considered the apostolic see or “see of Peter.” Although its true Cyprian applied the term also to the bishops in general, while calling Rome “the principal” or “chief” church.
Finally, the “Romans” in the paragraph refers to the bishops of Rome of course, which is the “throne” or “seat of Peter” and not just “Roman Christians” in general.
The final phrase is simply a matter of translation (faithlessness, or errors of faith, or perfidy, etc).
paragraph: to whom faithlessness could have no access
tract: whither no errors can come
So I conclude the statement is correct, although more of a paraphrase (like the “Rome has spoken, the case is closed” summary of Augustine, Sermons 131:10) depending on the accuracy of translation. Here is Jurgens translation:
“…they dare even to set sail…to the chair of Peter and the principal Church [at Rome], in which sacerdotal unity has its source…whose faith was praised by the preaching Apostle, and among whom it is not possible for perfidy [errors or perversion of faith] to have entrance.” (Epistle 59:14)
Here’s another translation from Edward Giles (an Anglican historian), the original Latin is from John Chapman:
Post ista adhuc pseudoepiscopo sibi ab haereticis constituto nauigare audent, et ad Petri Cathedram adque ad ecclesiam principalem unde unitas sacerdotalis exorta est ab schismaticis et profanis litteras ferre, nec cogitare eos esse Romanos, quorum fides Apostolo praedicante laudata est, ad quos perfidia habere non possit accessum
Translated this means, according to the Anglican scholar Giles:
“After all this, they yet in addition, having had a false bishop ordained for them by heretics, dare to set sail, and to carry letters from schismatic and profane persons to the chair of Peter, and to the principal church, whence the unity of the priesthood [sacerdotal unity] took its rise [or has its source]. They fail to reflect that those Romans are the same as those whose faith was publicly praised by the apostle, to whom unbelief [or error, heresy, perversion of faith] cannot have access.” (Epistle 59:14; from Giles, Documents Illustrating Papal Authority, page 60)
St. Cyprian on the Church and the Papacy by John Chapman