This seems to me to be a fit. The relative sizes of the surfactant protein A molecules can be aligned quite easily to the densities, layering and periodicity of the alveolar type II cell inclusions in the RER that I have seen in some of the randomly gathered electron micrographs from studies with guinea pig, ferret and mongrel dog.  Surfactant protein D is almost twice the length of surfactant protein A, at least according to published data and also images from google searches, and would only have a single band in the center for a periodicity.  So surfactant protein D doesn’t fit very well into the banding pattern in the RER of some type II cells.  I can count (depending upon section thickness and orientation) anywhere from three to 9 bands in any period, which fits nicely with four bands of 18-mers of surfactant protein A, accounting for spotty densities of the intermediate lines, and the dark bands where the carbohydrate recognition domains would appear clustered.

This short video takes one of the most detailed image of a profile of RER from a guinea pig type II cell (routinely processed for TEM worked up for a different study entirely)  that I have found in my collection of micrographs,  which is shown in the background, then the fading in is an image of the trilaminar membrane (in good resolution and the relative size is maintained, and the molecular arrangement of surfactant protein A that might be found in these  heterotrimers when they are assembeled into the 18-mer.  (Look at this article for a pretty nice review of the collectins, including SP-A and SP-D molecules –S0REN HANSEN and UFFE HOLMSKOV. Structural Aspects of Collectins and Receptors for Collectins. Immunobiol.,vol.199,pp. 165-189(1998))