Do I have to change the cross memeber?

[Nima]

Hi guys:
While I am messing with my interior, I am also gathering info about front suspension and disck brakes. I have read lots of good info here about this common upgrade but one thing that I am confused,still!!, is if I have to change the crossmember. My truck is 67 3/4 ton with drums all around. The quality of ride doesn't bother me much since I don't take it for long ride. I just want to rebuild the front end and switch to disck barke at the same time. I read the articles that I can/should change everything from a-arms all the ways down. Can I just use 1/2 parts without changing crossmember? If not, how about if I upgrade to 73+ model 3/4 ton? Another question now, Is it a big difference in price between 1/2 ton and 3/4 ton parts?
All these questions are an effort to avoid to chage the crossmember since to me this exchange is very involved and I am usually working alone. Thanks