Please consider the car as a system. A clear and attainable outcome has to be established and the parts that make up each subsystem must be selected to be complementary to each other and the desired outcome. A good analogy may be selecting the components to build a good audio system. Everything must work well together.
Some things to consider:
How do you REALLY want to use the car?
Is originality a consideration?
Do you want the engine to run on pump gas, what octane?
Does fuel consumption matter?
What is the budget?
How much of the work can you do?
Do you want to upgrade incrementally or all at once?
Whatever engine and power level you decide on, the transmission, differential, wheels/tires, brakes, and cooling systems must support the power level and RPM band of the engine. An example of what won't work well is the 375 HP engine with a stock C-4, a 1500 stall convertor, and a 2.75:1 gear in an open differential.
A 306 CID engine making 375 HP is harder to live with on the street than a 357 CID engine making 375 HP. Higher idle speed, less engine vacuum, less low RPM torque, cruise RPM, and higher convertor stall speed are some issues to consider when using the smaller displacement engine. It all depends on what you want, can afford, and can live with. That is why establishing the outcome carefully and realistically is vital. Whatever you decide to do I would avoid the "off the shelf complete package, one size fits all" solution. It is like a "universal" part for a car. Universal in this case means there isn't a single car in the universe that the part will work well on. I've never seen this approach yield more than mediocre results. There are simply to many variables involved for that approach to work well. Components selected for your exact application will yield better results.
If you can give us some more information about the car as it is and what your desired outcomes are we can and will help you get what you want. Sorry for the long response. You said you were new to this and I wanted you to know how deep the water was before you jumped in. Chuck