The telescope efficiencies (main beam and aperture efficiency) are given in Appendix A of The 30m Manual, the IRAM Newsletter Nr. 18 (November 1994) and a one-page IRAM 30m Telescope System Summary (available at http://www.iram.es/Telescope/systsumm.ps).
Beware of possible interference of the 230G2 LO into the 3 mm receivers. The 230G2 receiver cannot be operated with the 2 mm receiver, since both receivers use the same control box and polarization. Switching from one receiver to the other is not straightforward. Please specify in the proposal form whether you choose to use the 2 mm receiver or 230G2.
At 1.3 mm (and a fortiori at shorter wavelengths) a large
fraction of the receiver radiation pattern is distributed in an error
beam (which can be approximated by two Gaussians of HPW 
and 800'' -- see A&A 274, p.144-146 for more details).
Astronomers should take into account this error beam when converting
antenna temperatures into brightness temperatures. The effect is
particularly important at 0.8 mm, where the power radiated in the
`first' error beam 
is twice larger than in
the main beam.