The infrared optical conductivity of Rb3C60 and K3C60 and the temperature-dependent penetration depth of K3C60 are Calculated within a model for the pairing interaction which includes the possibility of coupling to both intra- and intermolecular phonons. It is found that excellent agreement with experimental data only occurs for coupling to high frequency intramolecular phonons, with an impurity scattering rate in the near-to-dirty limit. Strong coupling to low frequency modes is incompatible with the optical data.