Mechanical noob here. Any way these could be easily adapted for the 1500?
http://www.ebay.com/itm/Indian-Motorcycle-Billet-Rear-Passenger-Floor-Boards-/261145381140?pt=Motorcycles_Parts_Accessories&hash=item3ccd7a4914&vxp=mtr
Mounting holes on my Drifter are square, These look round with some kind of locating pins.? Would probably be adaptable by either drilling holes for the pins, if the rounds would or could be made to fit in the square hole ( please no round pin square hole comments) on the Drifter mount or possibly make a small square adapter with the pins holes to flush out the Drifter mount. I guess it depends on how creative you can be. As a Drifter owner Creative is a must for any mods as these bikes are seriously ignored when it come to accessories.
I don't exactly know what the 1500 passenger mounts are like, but the floorboards you are looking at look to me like "clevis mount" style. I had an earlier post about passenger boards on my 800:
http://www.vulcandrifterriders.com/forum/index.php?topic=17096.msg28632#msg28632
Clevis mounts are common on harley's I believe. You might be able to find some universal clevis mounts, like the ones I had (see previous post) that you could make work.
Or kuryakyn might make a mount that would bolt-on.