use any holes on the rail you want, make them closer like I pic below.  They will be secured by the Phils Rack when it is tightened on top also for added strength.

This would appear to solve the op's problem allowing him to use the backrest and topcase he already has.

Yea, maybe he will choose to do it and document with photos for future searches..hint hint..

The bike I just bought has a bakup USA backrest on it, I wouldn't have picked this one if I was buying a backrest.

Thanks for all the advice and I will be sure to document and post what I figure out.

Jason

Good luck, look forward to it.  It is an expensive backrest so hopefully you can make it work.  You have a nice bike there, very clean and original.

Getting closer to an answer to my problems. Got a Corbin seat on the way and have the V46 mounted with the SW-MOTEC plate but I don't see on Phils site where you can buy the rails. Do you have to buy the plate to get the rails?

Jhanks,

Jason

The plate looks flat with holes.  As I said you may need to drill 4 more holes for maximum clearance but that it up to you.  You can use Phils rack with the SW Motech kit that allows a Monokey box to be used.  Order of install

1. Phils rails.
2  Use closest two sets available holes to seat for the Backrest plate
3  Use the SW kit on a Phils rack and use the farthest set of holes for Phils Rack. 

Look at my picture and you will see I mounted the rails, Custom World Backrest plate, and then Phils rack with the SW kit on top.  You may need to customize the install a little but if mine worked so should this.  As a matter of fact the new plate AST is using looks identical to my Custom World plate.  I had to open up the holes a tiny bit to get it perfect.  You are better off ordering a CUSTOM WORLD backrest that chancing anything with AST



You can see the threaded hole here your closest set of holes on the backrest plate will bolt to, the backrest plate goes below Phils rack and on top of his rails.  It is not installed in this photo but you can see where it will

Here is the new plate that looks just like the Custom world but the old should work if you have it

Here is the three parts together.  Phils rails to bike mounts, Custom Worls backrest plate, then Phils monokey rack setup

The backrest without the box attached

JASONCP4:  I don't advertise the rails, I make them to-order and sometimes people have different needs. Also, the rails CAN be reversed to put more rmovement forward.