QEV's would be the obvious one, the ram is a personal choice not really a performance thing despite what some will tell you...to qualify that I will say in light of the modern rams
You might want to change the bolt..again personal choice. the feed collar is an area to look at as several are now available with a locking collar so no sanding of the hoppers is needed. A barrel set of some sort would be a good addition I won't say which, as everyone thinks something differnt about barrels.