Couple of things:
Lister make recommendations about pipe sizes and distances for engines that are piped to the outside, both for exhaust and for cooling air if air cooled.
Swept 2" bends are readily available over here in the UK, material is quite decent but they are seamless or welded tube that has been machined, not castings, so quite light. Bigger stuff is also available.
The JP cast silencers are a thing to behold, they are 'huge' and effectively a big expansion chamber. We have a couple sitting outside, but they have been shot blasted and Zinc sprayed before powder coating so the weather doesn't affect them.
Lister silencers, cooling tanks and radiators are all in the Lister Data section of the website.
Peter