Hrspwer tips on older car

i am seriously considering buying a 1972(ish) buick skylark... a gs 455 is what im going for and nothing less but i am wondering if there is anywhere i can get parts to add some serious horsepower to this baby..... my father owned a 1972 buick skylark gs 455 and i want to bring one back into the family and i just want to think of aftermarket parts for horsepower beforehand or any tips on how to modify the engine at home and strip or add things to the engine...

thankyou so much for your help :)