Join Date: Dec 2000
Location: Toronto, Ontario, Canada
It's hit-and-miss on this; depends on the relationship between bridge height to body surface (eg: neck shim = raising bridge studs to get appropriate action, which brings the springs closer to the surface of the spring cavity in back).
When the Backstop was a current item, I believe the standard route for any RG/Radius/etc type guitar included the relief route to accomodate a Backstop - I have a good friend with an old RG5xx (originally HSS, no pickguard) and it includes the extra routing stock.
For suggestions; TheToneZone is quite right about altering the unit - although it probably wouldn't cause any structural problems, it would be a cause for concern for a potential buyer, if in fact you don't wind up liking the Backstop's change to your trem's movement (and my guess is, from what I've read, you won't; it will detract too much from your flutter, and stiffen up the over-all feel of the bridge.)
Then again, I'm sure you don't want to carve into the body, especially when you're not sure you'll keep it in there...
Is there a chance that you've got a thick neck shim in your neck pocket? If so, you /could/ go to the lengths of TEMPORARILY removing part or all of that thickness, and dropping the bridge further into the body to help create spring clearance over the Backstop. Get it set up quickly and well enough to tell if you'll actually like the Backstop in there. If so, do a little relief routing (it's not much, it's just because the spring cavity is shallower at the claw end...), or grind out a bit of the Backstop base plate. If not, you're left with a couple of small screw holes in the spring cavity, and a Backstop that will still re-sell for a good $ to the right buyer.
Hope this helps.