Page 8 (18 in downloaded pdf) of the report suggests that the Thurston company was involved. This company was owned by David Thurston who had earlier worked with Goodyear (where he was involved in the GA-1 Duck) as well as Grumman (G-65 Tadpole). He had also been responsible for the Colonial Skimmer, a 1947/48 design. It is this design that, as the C-2 Skimmer IV, has been used in the depiction for the inflatable float study. Twenty of these were built and Aerofiles suggests that one of these was used in the HRV programme (viz N1001L), mentioned on the same page of the report.
Colonial, btw, sold all its assets to Lake Aircraft Corp. which explains the strong likeliness to the Lake Buccaneer.
References for this information are Aerofiles (entry for Thurston) and Johnson, E.R., American Flying Boats and Amphibious Aircraft (pp. 221-223, 249-252 and 283-284
Also, the report talks about an inflatable vertical float. The ones that we discussed earlier (Gyrodyne and the PBM pics) are made of metal, as far as I can determine, and seemingly not inflatable.