I still stand by what I said BD. I have the highest respect astro355, but I have to politely disagree with the unlikely part of it (Yes I'm Paranoid. Hmm, Actaually, No, I'm careful).
-V6s are an odd ball firing engine, this odd ball firing order is what generates more heat than the V8s do with an even firing order which "internally" run cooler the V6s (being stock for both).
-Having said that, cast manifolds "hold" more heat than headers do and why you get the feeling of more heat from them. As for temperatures between the 2 (Cast Manifolds and Headers) the headers may not "hold" as much heat as the cast manifolds do, but they run at a "higher" temperature range than the cast manifolds.
That's why you can actually touch the cast manifolds when they are hot (If your quick and crazy enough of course) and not get burned as opposed to touching the headers where you will leave half your hand (skin) on the header pipe. It's this higher temperature range that the headers inherently run at that causes the heat issues mentioned above. The headers may not actually start a fire, but it will be responsible for it in one way or another (Ie: heat melting a wiring harness, Harness shorts out and the possibility of a fire starts from that, melted harness).
Headers are made of a much thinner material which in turn means it will heat faster and glow brighter than cast manifolds. Another thing to consider here with the later model vans (96+) is the size of the engine compartment as compared to the older style (95-) vans. Astro355s van has much more room at the bottom where the motor sits with his as what our vans have. If you can take a look at my gallery and his, you can actually see how much more room he has compared to ours. His sub-frame is smaller and the motor mounts and motor sit lower which in turn means better cooling or air flow over it compared to ours. Our motor and mounts sit up a bit higher and the compartment is smaller which in turn means less air flow over the engine for cooling (or more stationary heat).
I'm not trying to scare you here at all BD, I'm just trying to get you to see the whole picture when something like this is considered. The ultimate decision will be yours and Astro355 brought up a very good point about "Jet Coated"? or Ceramic Headers (maybe the same thing), that would be the best way to go for sure if you do decide to get headers made up. They run "much" cooler than stock metal headers.
I'm sure I have fired up a few people about this one, hehe. But that's my story and I'm sticking to it and the way the world is viewed from my eyes (always error on the side of caution).