One of the members, GreenMotoVan or something, had a great solution. He used flanged L-track and mounted the factory seat brackets to it. Transit seats can be found pretty cheap, since a lot of van conversion and mobility companies take them out and just toss them and the brackets.
Mounting the factory brackets to a cargo can be problematic and they stick up above the floor. Mounting the brackets to flush L-track that sits between the floor ribs perfectly allows the seat to be removed, and then a couple bolts removes the bracket leaving a flat cargo floor, WITH L-track tie-down capabilities! They went full length with the L-track, but the 100" piece can be cut in half to make two sections. The middle seat support on the bench seat is overkill, there is a 3" diameter steel tube spanning the width, so it can be removed with a wrench to make the seat slightly more mobile (it weighs 200lbs or more). Flanged L-track can be found online, I think I spent $60-70 for the track, plastic ends, and bolts; shipped. Flanged allows the flooring to be tucked under so you don't have to be as precise with the cuts in the flooring. And it really IS flat, it fits perfectly.
I took the advice and did this, I also cut the seat brackets shorter to removing tripping hazard (the long brackets hold the set in back as well on the passenger vans):
Yes, that was me. This link will get you to the pages
on my build thread where I'm doing the L-track and seats.
I would consider cutting back the brackets in the front also as they do indeed create tripping points. I was hesitant and errored on the safe side leaving them longer using max mounting distance with 3 studs per track.
Having the L-track in the floor is very useful if you haul cargo, bikes, or other things you want to anchor down. It's a lot of work laying it down but great to have later.
Look in the "for sale" section here for seats first, then eBay, etc. Shipping prices add up REALLY fast for seats as they are heavy. It cost me as much to ship my seats as I paid for the seats themselves. If I'd been more patient I would have searched out some closer and drove to pick them up. You also get to inspect them before buying which is a plus. But finding "pull out" seats for these vans is pretty easy. There are numerous shops buying them for conversions which end up with seats they don't want/need.
The 3 person seats are pretty heavy to move, I use a forklift when doing mine cuz I have one and often need to do it by myself. The 2 person seats are more manageable.
There is some variation in the seat brackets so try to get the ones that fit the seats you buy if you can.
I bought my L-track on Amazon and the seller's stock varies, but there are other places like US Cargo Control and Cargo Equipment that have it. Sometimes it comes down to shipping costs. I'm 90% sure all the track is the same stuff.
I would use these studs
though. They are by far the strongest I could find and they are well made. They are available from a few sources but the price doesn't change much. I've bought most of my L-track hardware from Cargo Equipment, either from their Amazon store or dealing with them directly. If you work with the directly you can get quantity and shipping options not listed on the Amazon store.
When you are laying the track take you time and measure very carefully making sure the track is parallel and not skewed front to back or you will have a hard time getting the seats to latch in properly. There is some room for adjustment when you bolt the brackets down to the L-track and I use a straight edge to line the brackets up before tightening them down.
There's a little trick on the seat latches, to keep the latch retracted pull the latch fully back/open and insert a 5/16 bolt into the holes in the seat frame just up a bit and it will keep the latch retracted. Do this on all of them and you can then easily remove the seats. I just leave the bolts in until I replace the seats. I set the seat down in position then remove the bolts allowing the latch to snap closed.
Here's a photo of a latch retracted with a bolt inserted.
The same works for the 2 person seats but they have grab handles on the latches where as you need to use needle nose pliers or a hook for the 3 person seats.