The stem of the future present participle when -ūrus is removed is usually (although not always) identical to the stem of the perfect passive participle and supine.
There might have been a difference of vowel length (at least originally) between the identically spelled forms of these two verbs: vinco forming victūrus with short i and vīvo forming vīctūrus with a long ī.
Although there seems to be little or no surviving evidence in the Romance languages of short i in vict- words from vinco, the etymology of vinco suggests that the vowel in the participle forms should be short: compare rumpo, rūpī, ruptus.
There is also apparently an Oscan form spelled víkturrai which Michel de Vaan says represents a borrowing of Latin Victoria (in the dative singular). Oscan has a separate letter transcribed í that represented a short i sound. While there isn't a guarantee that Victoria and the participle forms of vinco had the same vowel length, the name is related to the verb.
The Latin Language – a historical outline of its sounds, inflections, and syntax, by Charles E. Bennett, does support a short vowel in vict- for forms and derivatives of vinco, although noting that some prior sources designated a long vowel on the basis of some evidence:
victor, victus, victōria, etc.: ī Lewis, on the basis of repeated inscriptional markings, such as
vIctor, CIL. vi. 10056; 10115; 1058;
vIctorinvs, vi. 1058;
vIctoriam, vi. 2086;
invíctae, vi. 353. But with a single exception no one of these inscriptions can be shown to antedate the third century a.d.; and I quite agree with Christiansen (de Apicibus et I longis, p. 49) in the view that in the classical period the i was short; later, apparently, it was lengthened.
On the other hand, "The cycle without containment: Latin perfect stems", by Donca Steriade, 2012, describes vinco as having a perfect passive participle stem vīct- with a long vowel, attributing the length to analogical extension from the long vowel in the perfect form vīcī (page 44) This sources does not describe the evidence for ī in vīct-, or discuss dates, so possibly it could be harmonized with Bennett's suggestion quoted above of a post-classical lengthening.