No!
Flat tappet cam lobes are tapered, offset, or both. That's to promote lifter rotation for wear purposes. The roller lifter need to ride on a straight flat lobe. The pressure applied by a tapered lobe would tear apart a roller setup fairly quick.
1991 to 1993 la blocks are roller blocks 1994 blocks could be both ways but all 1994 motors have magnum heads but some blocks are drilled for la heads. So if you would have the want to put a la hyd cam in a magnum block the only difference is the length of the lifter bores
Exactly.Putting a flat tappet cam in a magnum block is one thing, running roller lifters on a flat tappet cam is another and that's what the OP is asking. No can do