I'd holler at the Polar Kraft factory folks to find out exactly what the difference is. The composite is something like HPDM that is used under the decks and trolling motor mount area for reinforcement and backing. Bigger has that throughout on his 1886. Not sure if the 1885 had it or not...that might be the 300# difference. The composite is a good thing. Makes for a strong deck that will not rot.
I was thinking the 1885 did not have a flat floor, but is tilted like that one you looked at some time ago. Could be wrong though, but I doubt anyone here can tell you in detail exactly what the difference between the two is. PK doesn't have a whole lot of market share compared to a lot of mfgs.
Wannabe...