Hardbags can be successfully mounted to universal or other soft bag loop mounts, but you must take care than your chosen bags and mounts are compatible, and the goal is always to get as tight a fit to the fender as possible, and not have them so close to the exhaust they melt or burn (though the heat from OE pipes back there is not extreme, as the rear OE pipes in back are actually heat shields for internal one inch exhaust (3 per side).
You must also cushion your mounts (like with rubber or poly washers) from loop mounts to bags so they can withstand bouncing around (esp when loaded with weight). I'd use them both inside and outside the mounts.
To get a decent matchup from bags to mounts, I'd measure the mounts carefully on the bike, then try to buy aftermarket bags that will be compatible with those measurements.
If you don't want to go through all this, the Tsukayu hardbags (Hong Kong) (either Strong or Jumbo Strong) will fit a Valk pretty well and come with their own mounts, but you still have to do your own particular measuring, drilling and lashup. The Tsukayu's are pretty good bags (fiberglass, heavier than OE plastic), but they do have a bit of a radical angle in front to miss shocks, but on the Valk that was unnecessary, and the space left looks a little wrong, but it's still OK.
If you will paint these bags to match, you should do all your drilling, mounting, and a full mock up to your satisfaction, and only then take them off and get them painted.
Another thing to remember is the Strongs (and most aftermarket hardbags) are hinged in front, and need to hinge-open clear of any added trunk or wide back seat on your bike.
Jumbo Strongs (lot of space, large but so is the Valk)
This sort of shows the more radical (than OE) cut-back angle on the front of the Strongs (from the OE bag shape).
