I would check with Dave at Genium before buying a cam. He can probably tell you if your cam will be too big or not...Even with 4 reliefs, it may not fit. IIRC, The performer RPM cam was too large to run w/o valve guides at least. Larger than that, (I THINK) I would have had to have the pistons cut. The 284hr has .530 lift IIRC. The Performer RPM is only .490 IF I remember correctly. I may not, so I would double check it. But ask Dave at Genium. (91Notch on here)

FWIW- I had the Performer RPM cam, and intake on my 302 before with a 750 Vac secondary along with modified heads. It made my 3000lb 67 mustang run high 12's off the bottle. The Jr.'s and Sr. heads are better than mine I'm sure.