Upvote:1
The rubrics for the pre-1955 Missale Romanum (PDF p. 326) seem to assume there is a front and back side of the cross, which could only be possible were there a corpus on it:
Completis Orationibus, Sacerdos…accipit a Diacono Crucem jam in Altari præparatam: quam, versa facie ad populum… etc.
The orations having been completed, the Priest…takes the Cross, already prepared at the altar, from the Deacon: which, [the cross] turned toward the people… etc.
It can also be inferred that the cross shouldn't be so big that it can't rest on the altar.