Local events don't care that much about weight or weighing anything. So if yours is a few ounces over none's the wiser since it doesn't much matter. Even at the Nats, unless you are a finalist in Masters or F3A, chances are pretty good that it won't be weighed. Except for this year, 2012, where Archie weighed everyone, (I think)

The Focus 1 was reasonably light regardless and unless it has been crashed a few times and pick up a pound or two, you shouldn't have much problem.

Headers and pipes are covered extensively herein
You may want to talk with Merle Hyde at Custom Hyde mounts, to see if he can build you one. I make my own