www.skidim.com will most likely save you on parts that you need to source. As for the other questions that depends on the model of boat and the engine as the exhaust outlet is specific to a small block or a big block, 3 inch diameter for the small block and 4 inch for the big boy. Depending on the set up as there are so many various ways the factory or even owners after the fact did their exhaust it will be difficult to give you a finite answer. I overheated my exhaust last year and it was caused by a faulty muffler so I had to replace the muffler, the flange and all the exhaust hose as well.
'86 Comp TS6M - Reborn 2016
Riding a HO Sports CX Ski