…It is improper to combine it with any other service as an integration, but to have one of the hours precede the proper eucharistic service (be it mass or a communion service) is fully within the bounds. …
No, it is not improper to combine the Liturgy of the Hours with Mass.
From the General Instruction of the Liturgy of the Hours:
“93. In particular cases, if circumstances require, it is possible to link an hour more closely with Mass when there is a celebration of the liturgy of the hours in public or in common, according to the norms that follow, provided the Mass and the hour belong to one and the same office.”
Then in n. 94 it describes how to link Mass and Morning Prayer.
Entrance song, or “introductory verse and hymn of morning prayer”.
Procession
Celebrant’s greeting
“one of the introductory rites is thus omitted.”
Psalmody of morning prayer, up to but not including the reading.
Penitential Rite omitted
Kyrie and Gloria, “as circumstances suggest”.
Opening Prayer of Mass
Liturgy of the Word as usual …
“After the communion with its communion song the Canticle of Zechariah,
Blessed be the Lord, with its antiphon from morning prayer, is sung.”
In paragraphs 94-97 there are more instructions on combining Mass with Evening Prayer and daytime hours.
So the liturgical book provides explicit instructions for combining the Liturgy of the Hours with Mass. There are no such instructions for combining it with a Communion Service.
References: Documents on the Liturgy 1963-1979, Liturgical Press, Minnesota, 1982, ISBN 0-8146-1281-4, page 1109.
Divine Office, published by E.J. Dwyer, Sydney, 1974, ISBN 085574233X, pages li-lii.