2.5" exhausts are probably too big for a 283, but they'll work OK. A 2" pipe provides better exhaust scavenging for a small engine, especially one with dual exhausts.
Jerry
I'm not finding any new ram horn style manifolds with a 2" center dump. Can I use a reducer? Reduce from 2.5" down to 2" and then 2" for the rest of the exhaust? I still need to decide what muffler to use. I think straight pipe might be annoying to the neighbors.
