Sounds right. A rule of thumb I have always heard was to keep the header tube diameter near the same as the exhaust valve diameter. With 1.88" ev, the 1 7/8" tubes should be perfect. What size collectors and primary exhaust pipes to the mufflers? I would run 3" collectors to 3" primary exhasut pipes. No more than 18" from collector to muffler. 2 1/2" exhaust pipe after the muffler. Use a crossover pipe before the mufflers of 3" diameter in the 'H' configuration. Flowmaster mufflers unless you are making over 550-600 hp then I would use Magnaflow mufflers (straight thru design). These are my opinions. Hope it helps.