In the abbreviated Dictionary of Christian Biography edited by Wace and online at CCEL there is an article on Linus. This refers to certain “acts of Linus” in the following terms:
Under the name of Linus are extant two tracts purporting to contain the account of the martyrdom of SS. Peter and of Paul. These were first printed in 1517 by Faber Stapulensis as an appendix to his Comm. on Saint Paul’s Epistles. … Linus does not profess to give a complete account of the acts of the two apostles. He begins by briefly referring to (as if already known to his readers) the contest of St. Peter and Simon Magus, his imprisonments and other sufferings and labours, and then proceeds at once to the closing scenes. The stories of the martyrdom of the two apostles are quite distinct, there being no mention of Paul in the first nor of Peter in the second. …
… The alleged cause of Agrippa’s animosity exhibits strongly the Encratite character common to Linus and the Leucian Acts. St. Peter, we are told, by his preaching of chastity had caused a number of matrons to leave the marriage bed of their husbands, who were thus infuriated against the apostle.
… St. Peter requests to be crucified head downwards, desiring out of humility not to suffer in the same way as his Master. A further reason is given,, that in this way his disciples will be better able to hear his words spoken on the cross, and a mystical explanation is given of the inverted position which bears a very Gnostic character. An alleged saying of our Lord is quoted which strongly resembles a passage from the Gospel according to the Egyptians, cited by Julius Cassianus (Clem. Al. Strom. iii. 13, p. 553 see also Clem. Rom. ii. 12), “Unless ye make the right as the left, the left as the right, the top as the bottom, and the front as the backward, ye shall not know the kingdom of God.” … The story of Peter’s crucifixion head downwards was in the Acts known to Origen, who refers to it in his Comm. on Gen. (Eus. H. E. iii. 1).
The second book, which treats of St. Paul, relates the success of his preaching at Rome. The emperor’s teacher, his hearer and close friend, when he cannot converse with him, corresponds with him by letter. …
Lipsius infers, from the coincidences of the tolerably numerous N.T. citations in Linus with the Vulg., that our present Latin Linus must be later than Jerome; … We conjecture the compiler to have been a Manichean, but he is quite orthodox in his views as to the work of creation, the point on which Gnostic speculation was most apt to go astray.
Now these are certainly obscure items, and my attention was drawn to them only in a forum.
The edition of Faber Stapulensis, “Epistole divi Pauli Apostoli”, 1517 is on Google Books here; the two letters of Linus are right at the back and start here. A modern edition by Lipsius is here. There is a lengthy introduction.
Pp.xiv-xv discuss the text as “Acta Petri et Acta Pauli gnostica” and begin:
The passions of Peter and Paul which bear the name of Linus, bishop of Rome, were first edited by Jacob Faber Stapulensis as an appendix to the commentaries on the letters of Paul, which appeared in 1512, reprinted 1515 or 1516.
On p.xvi he discusses reprints, apparently rather duff ones. Then:
The passion of Peter the apostle is said in many manuscripts to have been written in Greek by bishop Linus and handed down by the eastern churches. The same is said not only of the passion of Paul, but also of the Life of Peter which in the name of Abdiah [fertur] is inscribed in the manuscripts.
But he says that it certainly wasn’t written in Greek.
The discussion continues; on p.xix-xx is a list of (Latin) manuscripts of the “passion of Peter”; on p.xxiii-xxvi is a similar list of 78 mss for the “passion of Paul”, probably incomplete (he says). A stemma appears on p.xxxi. The text is on p.1-22, and p.23-44, respectively.
The text as printed seems to be 37 words on 5 lines, i.e. 7.4 words per line.
For the Acta Petri, the line count is:
11+22+21+22+25+28+28+19+19+19+16+18+27+15+15+17+27+23+14+12+15+21 = 434 lines
Which would be 3212 words. It’s probably the same for the Acta Pauli gnostica.
I don’t know that either text has ever been translated. Each could probably be done for about $200. But is it worth it? I suppose that, if they have encratite views, they must be ancient and so should be made available.