Well, I've noticed a fair bit of Modernist stuff in the St. Andrew Missal, questioning various traditions, etc., the lives of the saints.

There was a huge push for the "soul of the Church" theory (which Msgr. Fenton denounced as erroneous) with the intention of undermining EENS dogma.  Here's the thing about the Holy Ghost, namely, that the Holy Ghost is involved in EVERY one of the Sacraments and is also responsible for the actual graces received leading to one's conversion.  Holy Ghost is invoked for the Mass/transubstantiation, Holy Orders, Confirmation, and Baptism ... and also for various actual graces.  This pouring out of the Holy Ghost most likely refers to the Holy Ghost inspiring in them the good dispositions to accept what St. Peter was teaching and the intention to be baptized.  There's nothing more that can be read into it.  Clearly they weren't Confirmed here, since they weren't even baptized.  So what does an outpouring of the Holy Ghost upon them mean other than their receiving the graces for conversion?  Council of Trent clearly taught that the Holy Ghost is responsible for the actual graces that ultimately leads to justification even before justification.  Nowhere can it be inferred from this passage, nor from the Church Fathers' understanding thereof, that they were somehow now united to the "soul of the Church", a novelty which Msgr. Fenton (who believed in BoD, by the way) rejected and stated was also condemned by the teaching of Pope Pius XII.

BTW, this is also the reason why the NO Rite of Holy Orders is doubtful.  There's an invocation of the Holy Ghost that's separated in the NO Rite from the sacramental effect of conferring the priesthood.  Since the Holy Ghost could be invoked for any number of reasons, including giving the priest the actual graces to faithfully carry out his vocation, it's unclear that the Holy Ghost is being invoked for the purpose of making the ordinand into a priest.  This is precisely what removing the Latin ut did.

Isn't this another way to describe Baptism of Desire? What would happen to any of these men if they did not actually get baptized (although it was clearly their intent)?

Baptism of Desire refers to justification before Baptism.  All we read in the Sacred Scriptures is that the Holy Ghost came down upon them.  We don't know what effect the Holy Ghost had from the text alone, whether it's actually justification or the actual graces that precede justification.  These are two separate things.  What would happen to them if they did not get baptized, let's say if they died right there, is unknown and cannot be determined from just the text alone.

Actually, when defined as "justification before Baptism", Father Feeney also believed in that, just did not agree that it could lead to salvation without actual reception of the Sacrament.  Others disagree that there can be justification before Baptism. 

But the ultimate point is that none of this can be read into the passage where the Holy Ghost was poured out on them.  We don't know what "effect" it had on them.  St. Andrew Missal is reading into it the effect, but the Holy Ghost can have effects upon them short of justification and prior to justification.  So, for instance, if we've lost the state of grace through mortal sin, even if we have not made an act of perfect contrition and therefore are not in a state of graces, even our inclination or desire to go to Confession is an effect of the Holy Ghost, even if it doesn't lead immediately to justification.