"Can you point to a specific prohibition?"
I'm afraid I don't have an Altar Missal of the old rite handy to consult the rubrics.
Obviously, non-celebrating priests can be called in to help with the distribution of Holy Communion at the old Mass, but I don't recall seeing anything about deacons, sub-deacons or acolytes being permitted to do this.
Perhaps someone reading the thread might have a copy of Fortescue which they can consult?
To be honest, even in the N.O. I always receive our Lord on the tongue and try to avoid handling the Sacrament as much as possible, so maybe I am being over-cautious in my assumptions.
I'm afraid I don't have an Altar Missal of the old rite handy
Sure you do. Just go to Google and type in "Ritus Servandus". You'll find that the rubric mentions only the "sacerdos" in the distribution of Holy Communion. It does not forbid the substitution of a deacon or instituted acolyte. If that prohibition exists elsewhere, I'm willing to be informed. I'm thoroughly aware of the iconic significance of receiving the Sacrament from a priest, and would cheerfully agree that this is to be preferred. The exigencies of parochial life make this difficult, however. When several hundred persons present themselves at the altar rail, it puts quite a strain on a lone man who's not in ideal health. Then there's the purely practical matter of the time it would take for one man to communicate the whole congregation. Spare priests are scarce these days.
even in the N.O. I always receive our Lord on the tongue
As do I, and always have. I do not believe I've ever received in my hand in my life.
Are you a permanent deacon?
The 1917 CIC says that deacons are extraordinary ministers of Holy Communion. This seems to be a matter covered in the CIC; hence, the new rules in the 1983 CIC might now be the applicable ones?
Can. 845. § l. Minister ordinarius sacrae communionis est solus sacerdos.§ 2. Extraordinarius est diaconus, de Ordinarii loci vel parochi licentia, gravi de causa concedenda, quae in casu necessitatis legitime praesumitur.