I just looked at the pics in greater detail, and these are "the proportions don't quite look entirely right" thoughtis - but is that sat on 8" wheels? I am not writing this as a slagging thing, but i;d rather write it than you discover the hard and expensive way that dynamic load on a trailer is a lot higher than you might think.......
2 thoughts (this one based on bitter experience) is that to get 8" tyres rated for the sort of weight you would need for a rib, you might be cheaper buying a new trailer! (apologies if they are 10", but better I tell you than you discover the hard way & get the same thing as I did as I took my rib home form where I bought it. Suffice to say 8" tyres are normally rated for about 400 KG a pair (for the bl**dy expensive ones - most give up at about 300Kg) Anyhow, they last about 25 miles before they have a major blowout. And I mean no trace of the tyre, nasty rubber marks on the hull kind of a blowout......
As for the drawbar, (again, only judging from the scale of it vs the hitch on the pics)- My dinghy trailer has a similar sectioned drawbar and is rated for max 120KG (i.e only just man enough to carry a 470). It might be OK wobble & bend wise if you park a "V" support or two along it's length (I essentuially have a double drawbar, as it;s a Combi trailer) to keep the whole lot in tension, but having said that I have no idea how heavy your rib is.
All that aside, should you decide to start again, that trailer would probably be fine for a dinghy, I;d just be wary of something bigger sat on it.
And apologies again if my idea of scale is completely wrong.