new exhaust system

G'day guys,
I'm an Aussie currently living and working in Saudi Arabia. I've bought myself a 1982 C3 and while the car is in pretty good condition, the standard exhaust manifolds are both cracked. I can get replacement standard manifolds, but I've found a "performance" shop that can manufacture stainless headers and a complete stainless system.
Could anyone help me with the design of the system? What is the best size (length and diameter) collector box for the headers to go into? I would perfer to go with a single system, so what is the best size pipe to go from the collector box to the rear of the vehicle?
There is very little in the way of "performance" parts available here and importing anything would be prohibitvely expensive, so to get anything half decent, I'll have to have it made. Any help would really be appreciated. Thanx.

Sizing of the tubes and collectors will be dependant on engine displacement, horsepower and toruqe output. I have attached a link to a story that was done in a U.S. magazine that should help you in your quest for a stainless exhaust system. I believe it also gives some formulas for figuring sizes of tubes, collectors, and flow.

http://www.popularhotrodding.com/tech/0310phr_burns/index.html

Good Luck.