neuroscience - Carrying or packaging capacity of SAD B19 dG rabies virus

I'm wondering about the carrying capacity also referred to packaging capacity or loading capacity (how many base pairs can be packed efficiently into virions) of the pseudotyped rabies virus SAD-dG as described in the Wickersham, Callaway publications.

Wickersham, I. R., Finke, S., Conzelmann, K.-K., & Callaway, E. M.
(2006). Retrograde neuronal tracing with a deletion-mutant rabies
virus. Nature methods, 4(1), 47–49. doi:10.1038/nmeth999

Wickersham, I. R., Lyon, D. C., Barnard, R. J. O., Mori, T., Finke,
S., Conzelmann, K.-K., et al. (2007). Monosynaptic Restriction of
Transsynaptic Tracing from Single, Genetically Targeted Neurons.
Neuron, 53(5), 639–647. doi:10.1016/j.neuron.2007.01.033