There are very little replacement parts available for them and I don't want to be using time looking for and waiting for parts, I'd rather be able to enjoy a car not always be part shopping
I honestly can't think of any particular part that you could not obtain in a reasonable amount of time that would preclude from operating or enjoying an early a-body (frog body's being the exception).
exculpation being that said part may not be "correct" or NOS or perfect; it would however not inhibit the operation of the vehicle in any way or bring any less enjoyment in operation.