Sealing headers

I have been told to soak the header gaskets overnight in water then put them on... One main issue (at least with Chebbys) is that the majority of the headers have round ports (tubes are round, they leave then round at the flanges) and then they don't match the ports on the heads. How close to your headers match the ports on the head? I have actually taken a mig welder to the hookers on my Suburban and re-shaped the port on the flange to make then fit correctly.

another trick is to use allen head bolts with small tooth washers wherever you can get them to fit.