I own a canoe and kayak outfitting business on the side and I think that qualifies me to say a word or two.
All of the comments posted have been good but I would add a few things.
A used 9' kayak for $400 is either over-priced or a high performance white water boat and you don't want either of them. I suggest taking a pic of the kayak and or the pontoon and let us have a
You can even get the make and model number and we will look it up and see if the boat will work.