I dont know why the billet 10" cover exists. I DO know that i had one, years and years ago in my a606 Intrepid (which is the same as a 41te converter other than having a longer snout to reach into the pump). I had Precision build me a ~3300 rpm stall converter, and they sent it with a billet cover. I didn't specifically request it, but i got it. It cost me (me as in the transmission shop i was working at) only about $350 back then in ~06.