Don't know if it will work or not but I like the idea.
A friend of mine has a VTX 1800N and I love the rear fender.
I'm wondering if it would make changing the rear tire harder to do though.
When changing a rear tire I put my bikes on a lift after removing both pipes, then remove the wheel and final drive. Elevate the bike sufficiently and there's more than enough room to drop the assembly free - even with a skirted fender. The 'N part would make roadside tire changes on a Valkyrie a bit more difficult, I think.
If you have access to a VTX-N service manual, see what their removal process entails. The rear ends of these bikes are very similar to our Valks.