In theory at Dillon 450 is not that much different than a turret. With a turret the dies are in the top and the shell stays in the shell holder directly in line with the handle. You can do each step in batches by not rotating the turret which is how I do it when I'm developing loads on the turret. Or you can place one fired case in the shell holder and have a completely reloaded shell when you remove it by rotating the turret. With a 450 or 550 you don't rotate the turret you rotate the shell holder.

I say don't send the old priming mechanism in if you send the 450 back for overhaul because I've talked to a few who when the press came back had a new priming system installed. For me the updated priming and powder was WELL worth the money. I don't feel I change dies often enough to make the full upgrade worth the investment. When I load a caliber it's usually in batches of a couple thousand. If I'm only doing 100 or working up loads I use a turret.