You do what you want to. It's your car, your time, your money. The 3 into 1 headers will work for you. Years ago, one of my buddy's with a '69 Firebird ran them because the 4 tube were so hard to fit around power steering. He did not have any problems.
There are good header gaskets - give Jim Butler a call. He has them and is close to you. The big issue is the expansion and contraction of the flange. This loosens the header bolts and causes the gaskets to blow out. Use a quality header gasket and the new locking header bolts - not sure of the brand. They are advertised in all the hot rodding magazines.
Even if you stay with your stock exhaust manifolds, I don't think you will ever find a paint product that will never burn off. I am getting ready to paint my long branch manifolds with Bill Hirsch manifold paint. I will see how long it lasts.
You could always get your stock manifolds blasted and jet hot coated - big $'s though.
If you are up to installing the headers and modifying your exhaust, I say do it.
Have a good one. Let me know the next time you are coming up this way and you can stop by and see the progress on my engine rebuild.
