Like John says, you need to tell us what your budget is. For some people in today's economy a spark plug change isn't exactly "minimal". There is much that can be done but generally speaking more HP = more $$.
You also need to decide what you want the car to be. The 76 455/4 speeds were the last of the 455s from the factory so that in itself makes the car worth more in "stock" form. If future resale is of concern for anytime in the down the road you might want to weigh your options carefully now. But if you just want it hopped up and you care not what that might do to the desirability of the car to someone else, then there are a lot more options.
