Howdy Jacob, first of all good choice ! I did mine and I used 4'' I wish I would have went with 5 or even 6'', you can get all the parts at truck parts house, straight pipe is 10' length ells from 15* to 90* nice s/s flex's come in 2' length's clamps come in s/s aswell, wy's come in a variety of configurations all fittings and pipe is aluminized steel and very easy to mig with or without gas. I choose to powder mine no maintinance I don't have pics on line yet but I hope to soon. anyhow the stacks were a lot of fun to do and i'll tell you what, they sound cool too,all i'm running is my stock resinator, good luck with your cooling towers
Joe Moglia