Others may have another opinion, but I couldn't get the remflex gasket to keep from blowing out. Itd seal for a while, but then it blow out where the manifold was warped eventually. It was just too soft and too thick in places I think. I tried it 3 times.
Anywho, I'd say the best thing to do is to try to get the intake and exhaust faced as a bolted together assembly so it is super flat where it hits the head, then make sure all the spots where the washers for the bolts hit on the manifold ears are all the same thickness. So basically where each washer hits make sure when bolted down it pulls evenly on both parts of the manifold. I used a dermal tool and took my time doing it and it worked fine.
Lastly, Use a stock gasket..... and when you torque it, follow the book! It seems like really light torque but it works. Don't be tempted to over tighten or you'll warp the manifolds again and they'll eventually leak.
So anyways, mine (and I've only done one 2f) didn't stay reliably sealed until I did it with the stock gasket, machined flat, and with the washer surfaces all the same thickness. I think others have had good luck with the remflex stuff.