"Grumman Delivery Truck" was used to put all Step Van-like trucks at a time
I guess most of the others could be renamed to Grumman-Olson (only a few are listed as Grumman, with model names existing in the other category).
I'll start to clean these, if someone who can identify trucks could check the "Delivery Truck" to tell to what they should be renamed...
But for the LLV, on http://en.wikipedia.org/wiki/Grumman they list it as Grumman only, where the UPS truck is well listed as Grumman-Olson