Mate - if you type in 'load rating' into the search function, it returns 15 pages of replies.
I reckon in there will be the info you need.
As to whether the tyres are suitable for your needs - only you can decide, as only you have access to the van in question and the ACTUAL weight of it (although you'll need to go on a weighbridge to find this out....)
Anyone else's opinions will only be guesswork...........
Its quite simple really - the tyres need to be up to the limit of the van which is likely to be 2800kg or 3000kg, so ideally they will need to be 98 load rated or more (I think 98 is 750kg). In law its not about how much your van actually weighs on the day, but what is the maximum capacity.
Obviously what you do is down to you and we all cut a few corners here and there to get what we want at the right price etc.
Just be aware that it may easily become an insurance / legal issue one day and for the sake of an extra £10-£20 per tyre its not worth the risk in my opinion.
I have also seen quite a few lower profile / under rated tyres on vans showing early signs of splitting around the shoulder of the sidewall.
A personal choice at the end of the day mate, but I have 94 ratings on my van. 17" rims.
My van is a 2.5 TDi panel with a double seat in the back. We have a weighbridge at work and my van came out at 1820kg.
My insurance company have no problem at all with the rims or tyres. I'm with HIC. Adrian Flux weren't concerned when I asked them a while ago.
The rims are load rated van rims and came from www.raceandroad.com
You can check out their website and all the van info concerning safety, load rating, insurance etc. They provided the rims with the 94 rating.
Only my thoughts, but if you have any doubts, play it safe and go for the highest rating you can get. Driving with a nagging doubt isn't enjoyable T: