Modifying headers, what size collector should I use???

Thanks everyone.
Yes the headers at the dyno were 4 into 1 long tube. I am not sure of the pipe size though, they definitely looked bigger than my Tri-Y's
Seeing that I am not in a rush cause the snow will be flying here soon, I guess selling these headers and buying new ones would be the correct solution then!!!.
Saying that what do you think mine would be worth? They are ceramic coated and in very good condition. No dents or marks to speak of.
Then what would be the best header for my application???
The only down side to the TTI's is that I will have to replace the Z-bar and a couple other things that I already bought brand new and that adds another couple hundred bucks or so. Remember we are getting are butts kicked up here (in Canada) on the exchange right now.
At the end of this build I am not looking for the fastest race car I can make, but a real nice street car that is both quick and relable.
Thanks again
Butch.