Yes, those are .500 spine arrows. If they are shooting left, you need a heavier point. Like a 200-250 grain point, instead of a 150. It all comes down to an interaction between several factors:arrow stiffness, point weight, width of the handle of the bow, pow poundage and drawlength. So, just because your arrow is a 50 pound spine and you have a 50 pound bow, doesn't necessarily mean it will fly well. Traditional bows tend to have a wide handle, requiring a weaker spine. When I shoot these type of arrows, I use the "GT trad 1535", which is just like your arrow, but weaker- it's a .600 spine arrow.
So, if you want to make those shafts work, do not cut them shorter and use heavier heads. Or trade them for some weaker shafts.