Another 318 Thread

I would bet many of specs are quite similar, but, as inkjunkie mentioned roller and flat tappet are physically much different...
On flat tappet cam the lobe acts on the whole.904" diameter of the (very slightly convex) lifter face, a roller only on a virtual point (roughly centerline of lifter, contact moving only a tiny bit for or aft of that axis depending where on the lobe the roller is)....
Now if you could make your roller the same radius as that of the face of your lifter, your cams would be very similar... but I'm guessing your rollers would be about 9 feet in diameter at that point...
Oh, and that's not taking into account that your flat tappet lobes are also oh so slightly tapered from one edge to the other to keep those lifters turning/spinning in their bores...
I'm pretty sure you can get magnum cams with a pump snout by special order.