My 54HC has the same metal guard you are describing and it was definitely too close to the top of the pulleys to slide the belt through (mine is on an X754). I removed the two mounting bolts and replaced them with longer carriage bolts and nuts between the deck and plate so it is high enough to slide the belt through. There is no plastic part of the guard for this belt on my mower deck. It is still a PITA to slide the belt through and I still carry a wrench on the machine to loosen the nuts if needed but it is much easier than it used to be.