I really like that bike. Nice job on it. You guys that are familiar with the fender, how much work do you think is involved with making it work on the Valk?
If you only ride solo, just need the fender and support. Drill holes in the fender and support to match the holes on the Valk fender rails. Snip the connector off of the Valkyrie fender and solder to the harness on the F fender.
You can use C-clamps to hold the fender to mark where to drill. The fender may be a little to narrow or too wide to fit between the Valk fender rails, so you might have to manipulate it a bit... From the looks of the pic it's a pretty close match width wise.
Potential problems that I can think of:
The angle of the shocks on the VTX is probably a little different than the Valk, so don't expect it to match up perfect, but it looks pretty damn close from the pics. The bottom of the front of the fender (under the seat, forward of the shocks) may need to be trimmed for clearance, but there's no way to know until you mock up the fender. On my I/S, the rear of the driver seat is held down by a tab on the fender. I'm not sure how the standard seats mount (prolly the same way), but you may need to have a tab welded to the new fender to accept the mount on the Valkyrie seat. You could always remove the bracket from the Valkyrie seat and use a couple suction cups...

If you ever ride with a passenger you'll have to get creative with rear seat options. Might be able to use an F rear seat pan and go from there, or maybe get with a company like Mean City Cycles and see if they could help you out in that area. Complete F fenders are usually a little on the expensive side. Good luck with your project if you decide to go for it.