Save yer time and energy DennisM , since you call it a whatchamacallit , and say you might have a wack at it ,, it is a dead give away that you dont have either the milling machine or the required knowledge to operate it.
If in fact the part can actually be modified , and if it is hardened then it is doubtful , then a shop with the required machinery and skills is the only option open to you ,, yep that means $$ to do a nice job .
So here is an off the wall suggestion , how about just butchering the thing by welding the part in place ??
??
