A suggestion: regardless of which header/muffler acquired, have everything ceramic coated.
If that sounds expensive, calculate the cost of replacing this system everything 5 years or so
(depending on which part of the country you are in) and see if the coating and resultant extended
life that comes with that, offsets the replacement cost.

Disclaimer: this may not apply as much to OE/stock engine vans as much as it seems to
for vans with engine conversions, with which I have some experience. I've found that the
best (so far) exhaust system is made from mild steel then coated.

Bob