The rear long range volley sight arm fits with no issues. Your bigger problem will be your volley sight plate that has been ground. Without the short extension (your sis ground down) there really is nothing for a front volley sight pointer and spring to secure to. With the extension ground off, the front pivot screw (the one with two opposing holes for a spanner) will not have enough threads to screw into. I have attached a pic of an intact volley sight plate and spring. It is missing a front pointer and screw. You'll see how the extension is necessary for the spring and screw to fit to. As far as price goes, they're pretty spendy on this side of the world. I've seen the rear volley arms sell for over $100 USD, and the front volley assemblies go for around $150USD. Maybe some other in your area can give you a better idea.

Depending how skilled you are (or if you have any skilled friends), you may be able to tig weld some round stock into place, then drill, thread and notch for the volley pointer, spring, and screw.