Slant six exhaust pipes size?

Original pipes were 1-3/4" diameter from the manifold to the muffler, and either 1-3/4" or 1-1/2" from the (tiny 3" × 7") muffler to the tailspout. "Beancounter special" undersized pipes that cost a few cents less. If it's time to do the exhaust on your car, you'll have a much better result by doing like this instead of duplicating the underspecified factory pipes.
I wasn’t planning on redoing the entire exhaust system, I was wanting to get a new muffler to make it a little louder, and wanted to know what size inlet/outlet to get, I don’t know if it’s a 2.50 or what. Thanks!