ABSOLUTELY agreed with Techinspector1 on the use of flat tappet in big block! Been a hobbyist for many years and been doing so with BBC's since early 1970s and do not place myself in the camp of many of our experts on the site, but their information/EXPERIENCE is invaluable.
With availability of just about anything you could ever want in roller cams you will save considerable exposure to cam failure by using one. Even so, I still use Joe Gibbs or similar oil as insurance. I still have a block or two that have the remnants of failed flat tappet cams in them!