i think they are 1 5/8 and three inch collectors....but i'm not 100% possitive. I did it mainly because of the heat...and also to make it look nice uderhood.
yep, those are the same as what mine are. and let me tell you, they get HOT. my engine bay is so hot after the car is just running for a little bit, because of how high those headers sit.
the ceramic coating is a good idea. i'd do it with mine if i didn't want to never take them out ever again. (and if i had the money)